The film is based loosely on the life of the Irish Tenor, Josef Locke (1917-1999). The film's exposition begins in Liverpool's Irish community, with Micky O'Neil running Hartley's Night Club. Micky is a bit of a rogue, and although he considers Nancy Doyle his girlfriend, he seems conflicted in saying "I love you".
Micky attempts to win Nancy by booking a series of impostors, including Franc Cinatra, and a Mr X -- a Josef Locke impersonator -- who travels under the 'X' since the real Josef Locke is wanted in England for tax evasion. When Micky finds that Nancy's mother was Josef Locke's special girl in the 1950's, he tries to hook them up.
Micky loses his job, vowing to find the real Josef Locke and bring him back to England from his exile in Ireland, to perform and thereby to win back Nancy. The rest of the film covers Micky's search for Locke in beautiful Ireland, with a triumphant final performance of the real Locke at the about-to-be-torn-down Hartley's.
The closing minutes of the film have the bulldog policeman Jim Abbott closing in on Locke. "Is it or isn't it?", the motto of Mr. X, belies the ending where the final scam plays out.
The tunes are classic Locke, although sung by Vernon Midgley. (There is a CD called "Hear My Song" by original the Josef Locke singing of 25 of Locke standards.)