diff --git a/cmd/transpile/basepath.go b/cmd/transpile/basepath.go
new file mode 100644
index 0000000..4dddc40
--- /dev/null
+++ b/cmd/transpile/basepath.go
@@ -0,0 +1,64 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+
+	"github.com/spf13/afero"
+)
+
+// BasePathFs is an overloaded afero.BasePathFs that has a recursive RealPath().
+type BasePathFs struct {
+	afero.Fs
+	source afero.Fs
+	path   string
+}
+
+// NewBasePathFs returns a new BasePathFs.
+func NewBasePathFs(source afero.Fs, path string) afero.Fs {
+	return &BasePathFs{
+		Fs:     afero.NewBasePathFs(source, path),
+		source: source,
+		path:   path,
+	}
+}
+
+// RealPath returns the real path to a file, "breaking out" of the BasePathFs.
+func (b *BasePathFs) RealPath(name string) (path string, err error) {
+	if err := validateBasePathName(name); err != nil {
+		return name, err
+	}
+
+	bpath := filepath.Clean(b.path)
+	path = filepath.Clean(filepath.Join(bpath, name))
+
+	if parentBasePathFs, ok := b.source.(*BasePathFs); ok {
+		return parentBasePathFs.RealPath(path)
+	} else if parentBasePathFs, ok := b.source.(*afero.BasePathFs); ok {
+		return parentBasePathFs.RealPath(path)
+	}
+
+	if !strings.HasPrefix(path, bpath) {
+		return name, os.ErrNotExist
+	}
+
+	return path, nil
+}
+
+func validateBasePathName(name string) error {
+	if runtime.GOOS != "windows" {
+		// Not much to do here;
+		// the virtual file paths all look absolute on *nix.
+		return nil
+	}
+
+	// On Windows a common mistake would be to provide an absolute OS path
+	// We could strip out the base part, but that would not be very portable.
+	if filepath.IsAbs(name) {
+		return os.ErrNotExist
+	}
+
+	return nil
+}
diff --git a/cmd/transpile/category.go b/cmd/transpile/category.go
index 42a214d..d742eea 100644
--- a/cmd/transpile/category.go
+++ b/cmd/transpile/category.go
@@ -10,7 +10,7 @@ import (
 // NewCategory returns a new category for the given path in the given fs.
 func NewCategory(fs afero.Fs, cat string) Category {
 	return Category{
-		Fs: afero.NewBasePathFs(fs, cat),
+		Fs: NewBasePathFs(fs, cat),
 	}
 }
 
@@ -41,7 +41,7 @@ func (c Category) Puzzles() ([]int, error) {
 	return puzzles, nil
 }
 
-// Puzzle returns the Puzzle associated with points.
-func (c Category) Puzzle(points int) (*Puzzle, error) {
-	return NewPuzzle(c.Fs, points)
+// PuzzleDir returns the PuzzleDir associated with points.
+func (c Category) PuzzleDir(points int) *PuzzleDir {
+	return NewPuzzleDir(c.Fs, points)
 }
diff --git a/cmd/transpile/main.go b/cmd/transpile/main.go
index db2b0df..4aeec1e 100644
--- a/cmd/transpile/main.go
+++ b/cmd/transpile/main.go
@@ -86,20 +86,21 @@ func (t *T) PrintInventory() error {
 // Open writes a file to the writer.
 func (t *T) Open() error {
 	c := t.NewCategory(t.Cat)
-	p, err := c.Puzzle(t.Points)
-	if err != nil {
-		return err
-	}
+	pd := c.PuzzleDir(t.Points)
 
 	switch t.Filename {
 	case "puzzle.json", "":
+		p, err := pd.Export()
+		if err != nil {
+			return err
+		}
 		jp, err := json.Marshal(p)
 		if err != nil {
 			return err
 		}
 		t.w.Write(jp)
 	default:
-		f, err := p.Open(t.Filename)
+		f, err := pd.Open(t.Filename)
 		if err != nil {
 			return err
 		}
diff --git a/cmd/transpile/main_test.go b/cmd/transpile/main_test.go
index c37d305..25b304a 100644
--- a/cmd/transpile/main_test.go
+++ b/cmd/transpile/main_test.go
@@ -47,10 +47,11 @@ body
 	afero.WriteFile(fs, "cat0/21/puzzle.md", []byte("Answer: broken\nSpooon\n"), 0644)
 	afero.WriteFile(fs, "cat0/22/puzzle.md", []byte("---\nanswers:\n  - pencil\npre:\n body: Spooon\n---\nSpoon?\n"), 0644)
 	afero.WriteFile(fs, "cat1/93/puzzle.md", []byte("Answer: no\n\nbody"), 0644)
+	afero.WriteFile(fs, "cat1/barney/puzzle.md", testMothYaml, 0644)
 	return fs
 }
 
-func TestThings(t *testing.T) {
+func TestEverything(t *testing.T) {
 	stdout := new(bytes.Buffer)
 	tp := T{
 		w:  stdout,
@@ -75,8 +76,8 @@ func TestThings(t *testing.T) {
 	if err := json.Unmarshal(stdout.Bytes(), &p); err != nil {
 		t.Error(err)
 	}
-	if p.Answers[0] != "YAML answer" {
-		t.Error("Didn't return the right object")
+	if (len(p.Answers) != 1) || (p.Answers[0] != "YAML answer") {
+		t.Error("Didn't return the right object", p)
 	}
 
 	stdout.Reset()
diff --git a/cmd/transpile/puzzle.go b/cmd/transpile/puzzle.go
index 44271bc..2202e4c 100644
--- a/cmd/transpile/puzzle.go
+++ b/cmd/transpile/puzzle.go
@@ -7,7 +7,9 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"log"
 	"net/mail"
+	"os"
 	"os/exec"
 	"strconv"
 	"strings"
@@ -18,18 +20,159 @@ import (
 	"gopkg.in/yaml.v2"
 )
 
-// NewPuzzle returns a new Puzzle for points.
-func NewPuzzle(fs afero.Fs, points int) (*Puzzle, error) {
-	p := &Puzzle{
-		fs: afero.NewBasePathFs(fs, strconv.Itoa(points)),
-	}
-
-	if err := p.parseMoth(); err != nil {
-		return p, err
+// NewPuzzleDir returns a new PuzzleDir for points.
+func NewPuzzleDir(fs afero.Fs, points int) *PuzzleDir {
+	pd := &PuzzleDir{
+		fs: NewBasePathFs(fs, strconv.Itoa(points)),
 	}
 	// BUG(neale): Doesn't yet handle "puzzle.py" or "mkpuzzle"
 
-	return p, nil
+	return pd
+}
+
+// PuzzleDir is a single puzzle's directory.
+type PuzzleDir struct {
+	fs afero.Fs
+	mkpuzzle bool
+}
+
+// Open returns a newly-opened file.
+func (pd *PuzzleDir) Open(name string) (io.ReadCloser, error) {
+	// BUG(neale): You cannot open generated files in puzzles, only files actually on the disk
+	if _, err := pd.fs.Stat(""
+	return pd.fs.Open(name)
+}
+
+// Export returns a Puzzle struct for the current puzzle.
+func (pd *PuzzleDir) Export() (Puzzle, error) {
+	p, staticErr := pd.exportStatic()
+	if staticErr == nil {
+		return p, nil
+	}
+
+	// Only fall through if the static files don't exist. Otherwise, report the error.
+	if !os.IsNotExist(staticErr) {
+		return p, staticErr
+	}
+
+	if p, cmdErr := pd.exportCommand(); cmdErr == nil {
+		return p, nil
+	} else if os.IsNotExist(cmdErr) {
+		// If the command doesn't exist either, report the non-existence of the static file instead.
+		return p, staticErr
+	} else {
+		return p, cmdErr
+	}
+}
+
+func (pd *PuzzleDir) exportStatic() (Puzzle, error) {
+	r, err := pd.fs.Open("puzzle.md")
+	if err != nil {
+		var err2 error
+		if r, err2 = pd.fs.Open("puzzle.moth"); err2 != nil {
+			return Puzzle{}, err
+		}
+	}
+	defer r.Close()
+
+	headerBuf := new(bytes.Buffer)
+	headerParser := rfc822HeaderParser
+	headerEnd := ""
+
+	scanner := bufio.NewScanner(r)
+	lineNo := 0
+	for scanner.Scan() {
+		line := scanner.Text()
+		lineNo++
+		if lineNo == 1 {
+			if line == "---" {
+				headerParser = yamlHeaderParser
+				headerEnd = "---"
+				continue
+			}
+		}
+		if line == headerEnd {
+			headerBuf.WriteRune('\n')
+			break
+		}
+		headerBuf.WriteString(line)
+		headerBuf.WriteRune('\n')
+	}
+
+	bodyBuf := new(bytes.Buffer)
+	for scanner.Scan() {
+		line := scanner.Text()
+		lineNo++
+		bodyBuf.WriteString(line)
+		bodyBuf.WriteRune('\n')
+	}
+
+	puzzle, err := headerParser(headerBuf)
+	if err != nil {
+		return puzzle, err
+	}
+
+	// Markdownify the body
+	if puzzle.Pre.Body != "" {
+		if bodyBuf.Len() > 0 {
+			return puzzle, fmt.Errorf("Puzzle body present in header and in moth body")
+		}
+	} else {
+		puzzle.Pre.Body = string(blackfriday.Run(bodyBuf.Bytes()))
+	}
+
+	return puzzle, nil
+}
+
+func (pd *PuzzleDir) exportCommand() (Puzzle, error) {
+	bfs, ok := pd.fs.(*BasePathFs)
+	if !ok {
+		return Puzzle{}, fmt.Errorf("Fs won't resolve real paths for %v", pd)
+	}
+	mkpuzzlePath, err := bfs.RealPath("mkpuzzle")
+	if err != nil {
+		return Puzzle{}, err
+	}
+	log.Print(mkpuzzlePath)
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	cmd := exec.CommandContext(ctx, mkpuzzlePath)
+	stdout, err := cmd.Output()
+	if err != nil {
+		return Puzzle{}, err
+	}
+
+	jsdec := json.NewDecoder(bytes.NewReader(stdout))
+	jsdec.DisallowUnknownFields()
+	puzzle := Puzzle{}
+	if err := jsdec.Decode(&puzzle); err != nil {
+		return Puzzle{}, err
+	}
+
+	return puzzle, nil
+}
+
+func legacyAttachmentParser(val []string) []Attachment {
+	ret := make([]Attachment, len(val))
+	for idx, txt := range val {
+		parts := strings.SplitN(txt, " ", 3)
+		cur := Attachment{}
+		cur.FilesystemPath = parts[0]
+		if len(parts) > 1 {
+			cur.Filename = parts[1]
+		} else {
+			cur.Filename = cur.FilesystemPath
+		}
+		if (len(parts) > 2) && (parts[2] == "hidden") {
+			cur.Listed = false
+		} else {
+			cur.Listed = true
+		}
+		ret[idx] = cur
+	}
+	return ret
 }
 
 // Puzzle contains everything about a puzzle.
@@ -56,7 +199,6 @@ type Puzzle struct {
 		Summary string
 	}
 	Answers []string
-	fs      afero.Fs
 }
 
 // Attachment carries information about an attached file.
@@ -66,37 +208,19 @@ type Attachment struct {
 	Listed         bool   // Whether this file is listed as an attachment
 }
 
-func legacyAttachmentParser(val []string) []Attachment {
-	ret := make([]Attachment, len(val))
-	for idx, txt := range val {
-		parts := strings.SplitN(txt, " ", 3)
-		cur := Attachment{}
-		cur.FilesystemPath = parts[0]
-		if len(parts) > 1 {
-			cur.Filename = parts[1]
-		} else {
-			cur.Filename = cur.FilesystemPath
-		}
-		if (len(parts) > 2) && (parts[2] == "hidden") {
-			cur.Listed = false
-		} else {
-			cur.Listed = true
-		}
-		ret[idx] = cur
-	}
-	return ret
-}
-
-func (p *Puzzle) yamlHeaderParser(r io.Reader) error {
+func yamlHeaderParser(r io.Reader) (Puzzle, error) {
+	p := Puzzle{}
 	decoder := yaml.NewDecoder(r)
 	decoder.SetStrict(true)
-	return decoder.Decode(p)
+	err := decoder.Decode(&p)
+	return p, err
 }
 
-func (p *Puzzle) rfc822HeaderParser(r io.Reader) error {
+func rfc822HeaderParser(r io.Reader) (Puzzle, error) {
+	p := Puzzle{}
 	m, err := mail.ReadMessage(r)
 	if err != nil {
-		return fmt.Errorf("Parsing RFC822 headers: %v", err)
+		return p, fmt.Errorf("Parsing RFC822 headers: %v", err)
 	}
 
 	for key, val := range m.Header {
@@ -119,99 +243,9 @@ func (p *Puzzle) rfc822HeaderParser(r io.Reader) error {
 		case "ksa":
 			p.Post.KSAs = val
 		default:
-			return fmt.Errorf("Unknown header field: %s", key)
+			return p, fmt.Errorf("Unknown header field: %s", key)
 		}
 	}
 
-	return nil
-}
-
-func (p *Puzzle) parseMoth() error {
-	r, err := p.fs.Open("puzzle.md")
-	if err != nil {
-		var err2 error
-		if r, err2 = p.fs.Open("puzzle.moth"); err2 != nil {
-			return err
-		}
-	}
-	defer r.Close()
-
-	headerBuf := new(bytes.Buffer)
-	headerParser := p.rfc822HeaderParser
-	headerEnd := ""
-
-	scanner := bufio.NewScanner(r)
-	lineNo := 0
-	for scanner.Scan() {
-		line := scanner.Text()
-		lineNo++
-		if lineNo == 1 {
-			if line == "---" {
-				headerParser = p.yamlHeaderParser
-				headerEnd = "---"
-				continue
-			}
-		}
-		if line == headerEnd {
-			headerBuf.WriteRune('\n')
-			break
-		}
-		headerBuf.WriteString(line)
-		headerBuf.WriteRune('\n')
-	}
-
-	bodyBuf := new(bytes.Buffer)
-	for scanner.Scan() {
-		line := scanner.Text()
-		lineNo++
-		bodyBuf.WriteString(line)
-		bodyBuf.WriteRune('\n')
-	}
-
-	if err := headerParser(headerBuf); err != nil {
-		return err
-	}
-
-	// Markdownify the body
-	if (p.Pre.Body != "") && (bodyBuf.Len() > 0) {
-		return fmt.Errorf("Puzzle body present in header and in moth body")
-	}
-	p.Pre.Body = string(blackfriday.Run(bodyBuf.Bytes()))
-
-	return nil
-}
-
-func (p *Puzzle) mkpuzzle() error {
-	bfs, ok := p.fs.(*afero.BasePathFs)
-	if !ok {
-		return fmt.Errorf("Fs won't resolve real paths for %v", p)
-	}
-	mkpuzzlePath, err := bfs.RealPath("mkpuzzle")
-	if err != nil {
-		return err
-	}
-
-	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
-	defer cancel()
-
-	cmd := exec.CommandContext(ctx, mkpuzzlePath)
-	stdout, err := cmd.Output()
-	if err != nil {
-		return err
-	}
-
-	jsdec := json.NewDecoder(bytes.NewReader(stdout))
-	jsdec.DisallowUnknownFields()
-	puzzle := new(Puzzle)
-	if err := jsdec.Decode(puzzle); err != nil {
-		return err
-	}
-
-	return nil
-}
-
-// Open returns a newly-opened file.
-func (p *Puzzle) Open(name string) (io.ReadCloser, error) {
-	// BUG(neale): You cannot open generated files in puzzles, only files actually on the disk
-	return p.fs.Open(name)
+	return p, nil
 }
diff --git a/cmd/transpile/puzzle_test.go b/cmd/transpile/puzzle_test.go
index bbd5435..3f1788f 100644
--- a/cmd/transpile/puzzle_test.go
+++ b/cmd/transpile/puzzle_test.go
@@ -1,6 +1,8 @@
 package main
 
 import (
+	"bytes"
+	"io"
 	"strings"
 	"testing"
 
@@ -12,11 +14,12 @@ func TestPuzzle(t *testing.T) {
 	catFs := afero.NewBasePathFs(puzzleFs, "cat0")
 
 	{
-		p, err := NewPuzzle(catFs, 1)
+		pd := NewPuzzleDir(catFs, 1)
+		p, err := pd.Export()
 		if err != nil {
 			t.Error(err)
 		}
-		t.Log(p)
+
 		if (len(p.Answers) == 0) || (p.Answers[0] != "YAML answer") {
 			t.Error("Answers are wrong", p.Answers)
 		}
@@ -29,7 +32,7 @@ func TestPuzzle(t *testing.T) {
 	}
 
 	{
-		p, err := NewPuzzle(catFs, 2)
+		p, err := NewPuzzleDir(catFs, 2).Export()
 		if err != nil {
 			t.Error(err)
 		}
@@ -44,26 +47,27 @@ func TestPuzzle(t *testing.T) {
 		}
 	}
 
-	if _, err := NewPuzzle(catFs, 3); err != nil {
+	if _, err := NewPuzzleDir(catFs, 3).Export(); err != nil {
 		t.Error("Legacy `puzzle.moth` file:", err)
 	}
 
-	if _, err := NewPuzzle(catFs, 99); err == nil {
+	if _, err := NewPuzzleDir(catFs, 99).Export(); err == nil {
 		t.Error("Non-existent puzzle", err)
 	}
 
-	if _, err := NewPuzzle(catFs, 10); err == nil {
+	if _, err := NewPuzzleDir(catFs, 10).Export(); err == nil {
 		t.Error("Broken YAML")
 	}
-	if _, err := NewPuzzle(catFs, 20); err == nil {
+	if _, err := NewPuzzleDir(catFs, 20).Export(); err == nil {
 		t.Error("Bad RFC822 header")
 	}
-	if _, err := NewPuzzle(catFs, 21); err == nil {
+	if _, err := NewPuzzleDir(catFs, 21).Export(); err == nil {
 		t.Error("Boken RFC822 header")
 	}
-	if _, err := NewPuzzle(catFs, 22); err == nil {
+	if p, err := NewPuzzleDir(catFs, 22).Export(); err == nil {
 		t.Error("Duplicate bodies")
 	} else if !strings.HasPrefix(err.Error(), "Puzzle body present") {
+		t.Log(p)
 		t.Error("Wrong error for duplicate body:", err)
 	}
 }
@@ -71,11 +75,29 @@ func TestPuzzle(t *testing.T) {
 func TestFsPuzzle(t *testing.T) {
 	catFs := afero.NewBasePathFs(afero.NewOsFs(), "testdata")
 
-	if _, err := NewPuzzle(catFs, 1); err != nil {
+	if _, err := NewPuzzleDir(catFs, 1).Export(); err != nil {
 		t.Error(err)
 	}
 
-	if _, err := NewPuzzle(catFs, 2); err != nil {
+	if _, err := NewPuzzleDir(catFs, 2).Export(); err != nil {
 		t.Error(err)
 	}
+
+	mkpuzzleDir := NewPuzzleDir(catFs, 3)
+	if _, err := mkpuzzleDir.Export(); err != nil {
+		t.Error(err)
+	}
+
+	if body, err := mkpuzzleDir.Open("moo.txt"); err != nil {
+		t.Error(err)
+	} else {
+		defer body.Close()
+		buf := new(bytes.Buffer)
+		if _, err := io.Copy(buf, body); err != nil {
+			t.Error(err)
+		}
+		if buf.String() != "Moo.\n" {
+			t.Error("Wrong body")
+		}
+	}
 }
diff --git a/cmd/transpile/testdata/3/mkpuzzle b/cmd/transpile/testdata/3/mkpuzzle
index 9b73f3c..d7d868b 100755
--- a/cmd/transpile/testdata/3/mkpuzzle
+++ b/cmd/transpile/testdata/3/mkpuzzle
@@ -6,7 +6,7 @@ case $1 in
 {
     "Answers": ["answer"],
     "Pre": {
-        "Authors": "neale",
+        "Authors": ["neale"],
         "Body": "I am a generated puzzle."
     }
 }