"I am writing a story. It's a fairy tale," announces Tyra Ferrel in the opening moments of Equinox. And indeed it is: discovering the bequest of a dead bag lady, she investigates the destinies of twins separated at birth. But if it is a fairy tale, it is played like a thriller. And if it's a thriller, the mystery is an existential one. Confused? You will be.

Not so much representing the triumph of nurture over nature as the triumph of artistic symmetry over reality, Mathew Modine plays the twins with clearly delineated mannerisms. One represents light the shy mechanic Henry Potosa, complaining "My whole life seems to be taking place without me in it" - and one dark - the aspiring gangster Freddy Ace, proudly self-made but somehow only half formed. Throughout the course of the movie, the two, unknown to each other but clearly separate halves of a whole, slowly move together.

Of course, you wouldn't necessarily work all that out without my telling you. On first viewing Equinox can be a baffling experience, as you struggle to get hold of the disparate elements of the plot, wondering whether it is a film about schizophrenia or if you just missed something. But for once I think I am right in giving the core away. Equinox is better second time around (and still manages to be baffling). The pleasures of this quest for identity are in the margins, in a succession of beautifully played, neatly dovetailed performances and a world in which the exteriors match the psychological interiors of the characters.

Each seems to be trapped in a different era, living in a terrifying city where everyday fears keep people separate. Rudolph's most personal films always take place in this world at least a side-step from our own and are slow to yield up their secrets. In its dreamlike development, and its failure to fully resolve its inner dilemmas Equinox can be frustrating, yet the humour and humanity that imbue the characterisations, and the dark undercurrent that pulses throughout, make it a memorable and unusual experience. But chances are, that after this Equinox is over, you'll still be in the dark.

RATING:HHHH