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. His son, Rashid, wishes to marry Uzma, but they need her devout Muslim cleric stepfather's, Arshad Al-Masri, blessing. Mahmud agrees to put on the act of devout Muslim for the occasion.
Mahmud, while clearing out his recently deceased mother's house, stumbles across an adoption certificate. Mahmud learns he was actually adopted by his Muslim parents when he was two weeks old; his birth parents were Jewish, and his real name is Solomon "Solly" Shimshillewitz. This comes as a shock to Mahmud, who is somewhat anti-Semitic, exemplified by his relationship with his American Jewish neighbour, Leonard "Lenny" Goldberg.
During an argument with Lenny, Mahmud lets slip his ethnicity and his real name, and Lenny mentions a similarity to the name, Isaac "Izzy" Shimshillewitz, a local man, who may be Mahmud's biological father. Mahmud tracks his father to a Jewish old age home. He tries to visit, but a rabbi refuses him entry, saying it would be a shock for Izzy, a Jewish man, to see his son, a Muslim, and advises him to learn to act more like a Jew if he desires to see his father before he dies.
Lenny agrees to teach Mahmud what he knows about being a Jew, such as dancing like Topol and learning basic Yiddish, but the frequent trips to Lenny's house arouse Mahmud's family's suspicions, especially when Mahmud's kippah is spotted during a Muslim rally. Mahmud publicly burns the kippah in desperation as a symbol of his supposed hatred of Jews. 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 and Lenny attempt to see Izzy, but the rabbi still refuses to let Mahmud inside when he cannot say his Jewish Sh'ma or name the Five Books of Moses in Hebrew.
Mahmud and Lenny have a bitter argument and Mahmud storms off, vowing to tell his family the truth immediately, but when he gets home, he sees that Arshad, Uzma and their friends are already there. Arshad, impressed with Mahmud's supposed devotion to Islam after having seen him burn the kippah on TV, gives his blessing to Rashid and Uzma's union, but the police arrive, along with the media and a crowd of angry Jews and supportive Muslims, to arrest Mahmud for burning the kippah. In desperation, he yells out in front of everyone that he is Jewish, exonerating him of the crime. A disgusted Arshad leaves with Uzma and his friends.
Mahmud's family leaves him for his dishonesty, one of his colleagues at work resigns, and he starts drinking. He becomes suicidal, but is rescued by Lenny, who saw his announcement on the news. Mahmud goes to the old age home and demands to see his father, but learns that his father has already died. Mahmud is allowed inside Izzy's room where he finds a video of his announcement in Izzy's video machine, which Lenny had sent Izzy. 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.
Mahmud appears at Arshad's next rally and delivers a speech on behalf of himself, Jewish citizens and Muslims. Mahmud also tells the crowd of another discovery which he's made: Arshad is actually Gary Page, who staged his own death following his fall from fame after a racist remark, resurfacing much later with a whole new identity as a devout Muslim cleric. Arshad escapes from the rally, comically dressed in his old Gary Page clothes. Rashid and Uzma, dressed in Hindu clothing, are married in a Bollywood style wedding, attended by both Muslims and Jews. Lenny has taken a job with the mostly-Muslim taxi firm at which Mahmud works.
Who plays Lenny?