Will, a rich, child-free, and irresponsible Londoner in his thirties, is in search of available women. He invents an imaginary son and starts attending single-parent meetings. As a result of one of his liaisons, he meets Marcus, an odd 12-year-old boy with problems at school. Gradually, Will and Marcus become friends, and as Will teaches Marcus how to be a cool kid, Marcus helps Will to finally grow up.