From DramaWiki

The synopsis says "Japanese man falsely imprisoned in Thailand" but the title of the original book is: "P.I.P. (Prisoner in Phnom Penh)", Phnom Penh is in Cambodge...

It is possible that the screenplay was based on the non-fiction novel. But it isn't unusual for the script to be re-written so that it'll appeal to the viewers. Groink 10:55, 2 May 2009 (UTC)