Romantic comedies usually fail when they can't establish a common ground between would-be lovers.

The sweet if insubstantial Australian movie "Griff the Invisible" doesn't have that problem. Before it's half an hour old, we're rooting for the geeky hero to connect with his equally geeky soul mate. Clearly, they're made for each other.

The first-time writer-director, Leon Ford, may be a little pushy about lining up their quirks and interests, but for the most part he knows what he's doing. He trips only during the finale, or rather the finales — each of them a little less convincing than the one that preceded it.

The easily bullied Griff (Ryan Kwanten) is an office worker with a rich vigilante fantasy life. At night, he dresses up in a rubber suit, rescues victims of a crime wave and talks just like Spiderman.

His exasperated brother, Tim (Patrick Brammall), has reached his limit, but Tim's unhappy girlfriend, Melody (Maeve Dermody), who declares herself "an experimentalist," recognizes Griff as her salvation. Once they start talking physics, parallel universes and the possibility of creating an invisibility suit, they're off in a world of their own.

Ford wants to take us with them, especially when his script insists on faith, confidence and low-rent special effects as cure-alls.

Kwanten, who plays the randy Jason on HBO's "True Blood," is so persuasively introverted in the office scenes that he could be auditioning for a new "Revenge of the Nerds" comedy. But the character has his sensual side, which Dermody draws out in a couple of episodes in which Griff and Melody discover how compatible they are.

It's almost enough to have two actors as well-cast and inventive as Kwanten and Dermody take these roles. Something clicks here. Physically as well as verbally, these kids are speaking their own language.

John Hartl: johnhartl@yahoo.com