London, 1961. The city's teenagers sing of the joys of Friday night, especially with a dance at the local youth club. There, Nicky Black sings a rock and roll number with his group, but Ernest, one of the members, reveals that the club is under threat of closure from the ruthless property developer, Hamilton Black. Unbeknown to his friends, Nicky is Hamilton's son, and Black senior gleefully accepts his offspring's challenge to save the club.

The group needs to raise £1,500 within a month in order to acquire the club's lease. Nicky composes a song, 'Lessons in Love', which he and his girlfriend Toni perform as a duet. A major record producer is interested in both the song and Nicky, but wishes to use his own female vocalist. Nicky refuses. Jimmy, another club member, tells the gang of a derelict theatre and, after trying on the costumes, Nicky and the others decide to restore the theatre and put on a fundraising show. They use an old RAF wireless transmitter to interrupt BBC and ITV programmes to advertise the 'Mystery Singer' - Nicky - who will be performing at the theatre.

The theatre's original owner is happy for the performance to go ahead, but shortly afterwards Hamilton buys it and informs the gang that he will now require more funds. On the eve of the big show, Nicky's friend Chris has the idea of gathering a gang of teddy boys to kidnap and rough up Hamilton. Learning of this plan, Nicky finally admits to being Hamilton's son and drives off to rescue his father. Members of the audience become restive at the non-appearance of the Mystery Singer and hurl rotten fruit at Jimmy and Ernest.

Meanwhile, Hamilton is easily defeating the teddy boys thanks to his mastery of judo. Nicky joins in, and after picking up a dazed Chris, the two return to the theatre in time for Nicky to perform a ballad and a rousing rock and roll number. Hamilton agrees that the youth club can stay and even deigns to dance with Nicky and Toni.