David Baddiel has turned his movie, The Infidel, into a musical. The set-up is so contrived and clumsy that it has a sweetness all its own. A golden-hearted London cabbie, named Mahmoud, discovers that he was adopted at birth and that his real parents were Jewish. This strikes him as intriguing rather than alarming, and he starts to investigate Judaism with the sort of disinterested curiosity of a man taking up astronomy after inheriting a telescope and a star-chart from an eccentric uncle.