いや、13冊かな
　https://gamebooks.org/Series/270/Show
　
　Gamebooks

1. Night of the Nazgul
2. The Legend of Weathertop
3. Rescue in Mirkwood
4. Murder at Minas Tirith
5. A Spy in Isengard
6. Treason at Helm's Deep
7. Mines of Moria
8. Search for the Palantir
9. Race from Rivendell
10. Pirates of Pelargir
11. Lost in the Lonely Mountain
12. Quest for the Palantir: The Ruins of Annuminas
13. Mission to Mordor