By Finlo Rohrer BBC News Online

It is a question many self-respecting psychiatrists could feasibly ask.

Is my patient really an alien from a dimly-lit planet orbiting the binary stars of Agape and Satori in the constellation of Lyra?

And it is a question asked in K-Pax of Kevin Spacey's character.

Spacey plays the mysterious Prot, committed to a mental asylum after some strange behaviour in New York's Grand Central Station.

Prot is soon explaining that he is from the planet K-Pax and will be returning there presently, travelling much faster than the speed of light.

Mary McCormack plays the archetypal trophy wife

While patients and staff await Prot's day of destiny, he starts to exert a beneficial presence on all around him through his tender words of wisdom.

He fascinates psychiatrist Dr Mark Powell, played by Jeff Bridges, who finds himself driven to uncover whether Prot is a delusional motivated by an incredible trauma or - shock horror - a genuine alien.

The asylum seems to be a model of good practice, and Dr Powell the most open-minded practitioner in the history of his profession.

It is hard not to warm to Bridges' affability, but he has little substance to work with in K-Pax outside discussions of the nature of delusions.

The central themes of the redemption of both a father's relationship with his family and the mentally ill pursue courses which are predictable.

Prot has inexplicable effects on fellow patients with cartoonishly simple disorders, lifted straight out of One Flew Over the Cuckoo's Nest.

Spacey's character comes across as irritatingly smug

But his Christ figure runs a poor second to Jack Nicholson's Randle P McMurphy.

And Dr Powell's family troubles - he works too hard and has an estranged son - are too thin to affect the audience.

Mary McCormack is given a wafer-thin romantic lead role where she is little more than an irked trophy wife with a sprinkling of lines.

And Spacey, for all his ability as an actor, only achieves zen-like levels of grinning smugness in the film.

The script is as warm, fuzzy and indistinct as the lighting.

Despite being based on a cult novel, there are holes in the plot so big a novice could navigate the QE2 through them.

And, although tense and nicely paced in some sections, the construction of the rather hurried ending does not bring satisfaction.

K-Pax is released in the UK on Friday 12 April