Tim Avery (Kennedy) is a wannabe animator who lives in a cartoonish house with his adorably perky wife Tonya (Howard). She wants a baby; he wants to remain irresponsibly goofy. Then their precocious dog Otis finds the lost mask of Loki (Cumming), Norse god of mischief, who's desperate to get it back. The hitch is that Tim and Tonya conceive their son (Falconer and Falconer) while Tim is wearing the mask, which means that Alvey is born with Loki's shape-shifting, trouble-causing powers.

Actually, the film starts promisingly, with a hilarious visit to a museum in which a curator (the bone-dry Stein) narrates the back-story and has an early encounter with Loki. But our laughter stops the moment the special effects kick in, because they go right over the top into meaningless mayhem. And it gets worse as the contrived story kicks in, replacing logic and characters with soulless computer-generated wackiness.

In the first film, when Jim Carrey put on the mask, his face went rubbery and silly. Here, poor Kennedy becomes a stiffly grinning, plastic-faced mannequin devoid of personality. Cumming gets lost in the swirling pyrotechnics. And Hoskins (as Loki's father Odin) gets lost in his overwrought make-up. Even the dog, easily the film's best actor, gets replaced by gonzo CGI. What's left is manic nuttiness devoid of plot or character. And it makes no sense. What struggling animator lives in a palatial suburban mansion? Without a computer? Why doesn't Tonya ever notice her son's odd behaviour? What kind of sadists name their son Alvey Avery?

It's unlikely that we'll see another film that goes so rapidly downhill. If the staggeringly awful rendition of Can't Take My Eyes Off Of You (I Love You Baby) doesn't make your flesh crawl, just wait for the offensive Mr Mom montage. Or the gut-wrenchingly yucky moral messages piled on at the end. Staggeringly awful.