Say It Isn't So puts a comically depraved spin on a classic love story: Boy meets girl; Boy falls in love with girl; Boy loses girl... when they learn they are siblings!

The Farrelly brothers are the duo responsible for Dumb & Dumber, Kingpin and Me, Myself & Irene, so a certain expectation comes with the name.

However, the Farrellys controlled every aspect of these films. With Say It Isn't So, they only produce, leaving both the writing and directing to first-timers.

The story follows nice-but-silly Gilly (American Pie's Klein), who falls in love with the beautiful Jo (Graham), only to be told, mistakenly, that she's his sister.

When Gilly discovers the error, he travels across the US aided by pilot Dig (Evolution's Jones), a double amputee with a leg up on some of the film's funnier moments, to stop Jo from marrying her wealthy bully of an ex-boyfriend.

But her mother (Forrest Gump's Sally Field) is prepared to go to any length to ensure that her daughter marries the man with the money.

Two-time Oscar-winner Field (Places in the Heart, Norma Rae, Mrs. Doubtfire) has the most outrageous role of her career as the foul-mouthed, white trash matriarch who persuades her daughter to abandon her feelings in favour of the shady millionaire.

Comparable to Something About Mary (another Farrelly triumph), it is filled with one crude joke after another as we follow our hapless hero from one disgrace to the next.

But the film often comes across as surprisingly sweet - if you can forgive its gross-out comedy.

Dominic Bloch