The film revolves around a British Muslim man who goes through an identity crisis when he discovers that he was adopted as a baby and born to a Jewish family.

[2] Mahmud Nasir is a husband, father and a British Muslim who listens to rock music, particularly the long deceased pop star Gary Page, and occasionally drinks alcohol.

Mahmud later attends a Bar Mitzvah with Lenny and unintentionally tells a very crude joke to the audience in broken Yiddish, only to be greeted with laughter from the attendees.

Mahmud's only solace is a sticker on the video with the name "Solly" on it, indicating that even after all these years, Izzy still remembered his long-lost son.

Rashid and Uzma are married, with the wedding attended by both Muslims and Jews while Lenny has taken a job with the mostly-Muslim taxi firm at which Mahmud works.

David Baddiel wrote The Infidel because he has "always been a fan of life-swap comedy (Big, Trading Places, etc)"; he "think[s] that people are terrified about race and religion, especially issues surrounding Muslims and Jews, and when people are terrified, what they really should do is laugh"; and he "love[s] Omid Djalili and his big funny face.

The musical later opened at the Theatre Royal Stratford East directed by the Artistic Director, Kerry Michael.

[6][7] The film was remade in India under the title Dharam Sankat Mein (crisis of faith), with the same basic premise, of a man raised Hindu finding out he was born into a Muslim family.