diff --git a/cmd/transpile/main_test.go b/cmd/transpile/main_test.go
index 352029b..c37d305 100644
--- a/cmd/transpile/main_test.go
+++ b/cmd/transpile/main_test.go
@@ -29,13 +29,13 @@ RFC822 body
 
 func newTestFs() afero.Fs {
 	fs := afero.NewMemMapFs()
-	afero.WriteFile(fs, "cat0/1/puzzle.moth", testMothYaml, 0644)
+	afero.WriteFile(fs, "cat0/1/puzzle.md", testMothYaml, 0644)
 	afero.WriteFile(fs, "cat0/1/moo.txt", []byte("Moo."), 0644)
-	afero.WriteFile(fs, "cat0/2/puzzle.moth", testMothRfc822, 0644)
+	afero.WriteFile(fs, "cat0/2/puzzle.md", testMothRfc822, 0644)
 	afero.WriteFile(fs, "cat0/3/puzzle.moth", testMothYaml, 0644)
-	afero.WriteFile(fs, "cat0/4/puzzle.moth", testMothYaml, 0644)
-	afero.WriteFile(fs, "cat0/5/puzzle.moth", testMothYaml, 0644)
-	afero.WriteFile(fs, "cat0/10/puzzle.moth", []byte(`---
+	afero.WriteFile(fs, "cat0/4/puzzle.md", testMothYaml, 0644)
+	afero.WriteFile(fs, "cat0/5/puzzle.md", testMothYaml, 0644)
+	afero.WriteFile(fs, "cat0/10/puzzle.md", []byte(`---
 Answers:
   - moo
 Authors:
@@ -43,8 +43,10 @@ Authors:
 ---
 body
 `), 0644)
-	afero.WriteFile(fs, "cat0/20/puzzle.moth", []byte("Answer: no\nBadField: yes\n\nbody\n"), 0644)
-	afero.WriteFile(fs, "cat1/93/puzzle.moth", []byte("Answer: no\n\nbody"), 0644)
+	afero.WriteFile(fs, "cat0/20/puzzle.md", []byte("Answer: no\nBadField: yes\n\nbody\n"), 0644)
+	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)
 	return fs
 }
 
@@ -58,7 +60,7 @@ func TestThings(t *testing.T) {
 	if err := tp.Handle("inventory"); err != nil {
 		t.Error(err)
 	}
-	if stdout.String() != "cat0 1 2 3 4 5 10 20\ncat1 93\n" {
+	if stdout.String() != "cat0 1 2 3 4 5 10 20 21 22\ncat1 93\n" {
 		t.Errorf("Bad inventory: %#v", stdout.String())
 	}
 
diff --git a/cmd/transpile/puzzle.go b/cmd/transpile/puzzle.go
index 41b1c60..44271bc 100644
--- a/cmd/transpile/puzzle.go
+++ b/cmd/transpile/puzzle.go
@@ -127,9 +127,12 @@ func (p *Puzzle) rfc822HeaderParser(r io.Reader) error {
 }
 
 func (p *Puzzle) parseMoth() error {
-	r, err := p.fs.Open("puzzle.moth")
+	r, err := p.fs.Open("puzzle.md")
 	if err != nil {
-		return err
+		var err2 error
+		if r, err2 = p.fs.Open("puzzle.moth"); err2 != nil {
+			return err
+		}
 	}
 	defer r.Close()
 
diff --git a/cmd/transpile/puzzle_test.go b/cmd/transpile/puzzle_test.go
index 4ef8191..bbd5435 100644
--- a/cmd/transpile/puzzle_test.go
+++ b/cmd/transpile/puzzle_test.go
@@ -1,6 +1,7 @@
 package main
 
 import (
+	"strings"
 	"testing"
 
 	"github.com/spf13/afero"
@@ -10,36 +11,71 @@ func TestPuzzle(t *testing.T) {
 	puzzleFs := newTestFs()
 	catFs := afero.NewBasePathFs(puzzleFs, "cat0")
 
-	p1, err := NewPuzzle(catFs, 1)
-	if err != nil {
-		t.Error(err)
-	}
-	t.Log(p1)
-	if (len(p1.Answers) == 0) || (p1.Answers[0] != "YAML answer") {
-		t.Error("Answers are wrong", p1.Answers)
-	}
-	if (len(p1.Pre.Authors) != 3) || (p1.Pre.Authors[1] != "Buster") {
-		t.Error("Authors are wrong", p1.Pre.Authors)
-	}
-	if p1.Pre.Body != "<p>YAML body</p>\n" {
-		t.Errorf("Body parsed wrong: %#v", p1.Pre.Body)
+	{
+		p, err := NewPuzzle(catFs, 1)
+		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)
+		}
+		if (len(p.Pre.Authors) != 3) || (p.Pre.Authors[1] != "Buster") {
+			t.Error("Authors are wrong", p.Pre.Authors)
+		}
+		if p.Pre.Body != "<p>YAML body</p>\n" {
+			t.Errorf("Body parsed wrong: %#v", p.Pre.Body)
+		}
 	}
 
-	p2, err := NewPuzzle(catFs, 2)
-	if err != nil {
-		t.Error(err)
+	{
+		p, err := NewPuzzle(catFs, 2)
+		if err != nil {
+			t.Error(err)
+		}
+		if (len(p.Answers) == 0) || (p.Answers[0] != "RFC822 answer") {
+			t.Error("Answers are wrong", p.Answers)
+		}
+		if (len(p.Pre.Authors) != 3) || (p.Pre.Authors[1] != "Arthur") {
+			t.Error("Authors are wrong", p.Pre.Authors)
+		}
+		if p.Pre.Body != "<p>RFC822 body</p>\n" {
+			t.Errorf("Body parsed wrong: %#v", p.Pre.Body)
+		}
 	}
-	if (len(p2.Answers) == 0) || (p2.Answers[0] != "RFC822 answer") {
-		t.Error("Answers are wrong", p2.Answers)
+
+	if _, err := NewPuzzle(catFs, 3); err != nil {
+		t.Error("Legacy `puzzle.moth` file:", err)
 	}
-	if (len(p2.Pre.Authors) != 3) || (p2.Pre.Authors[1] != "Arthur") {
-		t.Error("Authors are wrong", p2.Pre.Authors)
-	}
-	if p2.Pre.Body != "<p>RFC822 body</p>\n" {
-		t.Errorf("Body parsed wrong: %#v", p2.Pre.Body)
+
+	if _, err := NewPuzzle(catFs, 99); err == nil {
+		t.Error("Non-existent puzzle", err)
 	}
 
 	if _, err := NewPuzzle(catFs, 10); err == nil {
-		t.Error("Broken YAML didn't trigger an error")
+		t.Error("Broken YAML")
+	}
+	if _, err := NewPuzzle(catFs, 20); err == nil {
+		t.Error("Bad RFC822 header")
+	}
+	if _, err := NewPuzzle(catFs, 21); err == nil {
+		t.Error("Boken RFC822 header")
+	}
+	if _, err := NewPuzzle(catFs, 22); err == nil {
+		t.Error("Duplicate bodies")
+	} else if !strings.HasPrefix(err.Error(), "Puzzle body present") {
+		t.Error("Wrong error for duplicate body:", err)
+	}
+}
+
+func TestFsPuzzle(t *testing.T) {
+	catFs := afero.NewBasePathFs(afero.NewOsFs(), "testdata")
+
+	if _, err := NewPuzzle(catFs, 1); err != nil {
+		t.Error(err)
+	}
+
+	if _, err := NewPuzzle(catFs, 2); err != nil {
+		t.Error(err)
 	}
 }
diff --git a/cmd/transpile/rfc822.md b/cmd/transpile/rfc822.md
deleted file mode 100644
index e972932..0000000
--- a/cmd/transpile/rfc822.md
+++ /dev/null
@@ -1,15 +0,0 @@
-Author: neale
-Answer: moo
-
-A MOTH file
-===========
-
-This is a moth file, woo wo!
-
-# A MOTH file
-
-* moo
-* moo
-* moo
-* squeak
-
diff --git a/cmd/transpile/yaml.md b/cmd/transpile/testdata/1/puzzle.md
similarity index 100%
rename from cmd/transpile/yaml.md
rename to cmd/transpile/testdata/1/puzzle.md
diff --git a/cmd/transpile/testdata/2/moo.js b/cmd/transpile/testdata/2/moo.js
new file mode 100644
index 0000000..09de201
--- /dev/null
+++ b/cmd/transpile/testdata/2/moo.js
@@ -0,0 +1 @@
+console.log("Moo.")
diff --git a/cmd/transpile/testdata/2/moo.txt b/cmd/transpile/testdata/2/moo.txt
new file mode 100644
index 0000000..e31bd82
--- /dev/null
+++ b/cmd/transpile/testdata/2/moo.txt
@@ -0,0 +1 @@
+Moo.
diff --git a/cmd/transpile/testdata/2/puzzle.md b/cmd/transpile/testdata/2/puzzle.md
new file mode 100644
index 0000000..540b816
--- /dev/null
+++ b/cmd/transpile/testdata/2/puzzle.md
@@ -0,0 +1,25 @@
+Summary: A legacy RFC822-formatted puzzle
+Author: neale
+Answer: moo 0
+Answer: moo 1
+Answer: moo 2
+Pattern: moo *
+Hint: Use the source, Luke.
+KSA: none
+File: moo.txt
+File: moo.txt moo-two.txt
+File: moo.txt moo-too.txt hidden
+Script: moo.js moo.js
+
+A MOTH file
+===========
+
+This is a moth file, woo wo!
+
+# A MOTH file
+
+* moo
+* moo
+* moo
+* squeak
+
diff --git a/cmd/transpile/testdata/3/mkpuzzle b/cmd/transpile/testdata/3/mkpuzzle
new file mode 100755
index 0000000..9b73f3c
--- /dev/null
+++ b/cmd/transpile/testdata/3/mkpuzzle
@@ -0,0 +1,23 @@
+#! /bin/sh
+
+case $1 in
+    "")
+        cat <<'EOT'
+{
+    "Answers": ["answer"],
+    "Pre": {
+        "Authors": "neale",
+        "Body": "I am a generated puzzle."
+    }
+}
+EOT
+        ;;
+    moo.txt)
+        echo "Moo."
+        ;;
+    *)
+        echo "Error: no such file: $1" 1>&2
+        exit 1
+        ;;
+esac
+    
\ No newline at end of file