Once upon a time, Cruise was the world's undisputed alpha movie-star. But then he lost his crown to DiCaprio. So just what went wrong for him - and can he get back on top? Head to head:

Tom Cruise and Leonardo DiCaprio  Head to head: Tom Cruise and Leonardo DiCaprio Photograph: KIYOSHI OTA/REUTERS

There is a story playing out right now in Hollywood that epitomises the perils of fame, the precariousness of success and the dangers of celebrities left unguarded. You can imagine it framed in the blockbuster vernacular, the voiceover delivered in the gravelly, portentous boom.

That comes as standard in every trailer: "Two men. One dream: to be the king of the multiplexes. But they dared to want more. They dared to want . . . integrity." Then the names and faces of two Hollywood behemoths would flash up on screen. Tom Cruise. Leonardo DiCaprio. Who will prevail?