Unrivaled as the most inventive and wildly conceptual movie of 1999, there's just no way to explain "Being John Malkovich" without it sounding too weird to be for real.

The daring feature debut of music video and commercial director Spike Jonze, the film stars a disheveled John Cusack as an unemployed, master puppeteer and social malcontent who discovers a portal into the mind of actor John Malkovich when he takes a peon filing job at an esoteric office on the 7 1/2th floor of turn-of-the-Century Manhattan high-rise.

See? I told you.

The portal opening is a pint-sized door hidden behind a filing cabinet, which Cusack crawls through and winds up a tourist inside Malkovich's head -- seeing the world through his eyes for 15 minutes before being blasted out the other side of this metaphysical rift and landing in a ditch beside the New Jersey Turnpike.

This very dark, off-the-wall comedy follows the increasingly erratic Cusack's attempts to exploit and control Malkovich like one of his eerie marionettes, using the portal to impress a sexy, heartless co-worker (Catherine Keener), who in turn begins to manipulate Cusack and his plain Jane wife (played by Cameron Diaz in a frizzy wig and no make-up), who have both become smitten with her.

In "Malkovich" Jonze creates an off-kilter world, reminiscent of a Terry Gilliam movie. Case in point, the 7 1/2th floor -- a sliver of reality limbo, with five-foot ceilings and a quizzical office staff -- which can only be reached by halting the building's elevator and crow-barring open the doors.

The picture is jam-packed with such oddities, from Cusack's disturbingly grim and hollow-eyed marionettes (which he uses to act out exacting fantasies about Keener) to sympathetic Diaz's menagerie of stray animals (she brings home sickly monkeys, iguanas, ferrets and parrots from her job at a pet store) that populate their dingy basement apartment.

And it only gets stranger after Keener and Cusack start selling trips through his noggin for $200. Keener soon finds and seduces John Malkovich. Then both Diaz and Cusack begin stepping inside him so they can be a party to taking Keener to bed, leaving Cusack feeling unloved and Diaz in a sexual identity crisis.

It isn't long before the Malkovich (playing himself with astute self-mockery) catches on that something is badly amiss inside his mind, follows Keener to the 7 1/2th floor and enters the portal himself, entering what is probably the weirdest, creepiest, funniest vision of unleashed subconscious ever put on film.

The always-enjoyable John Cusack is prophetic here as the mousy, miscreant puppeteer who, after a few trips through the portal, learns to manipulate Malkovich as if he has him on a string, struggling for control over his body (Malkovich hilariously tosses himself around like a rag doll and channels Cusack with adroit precision) and soon trying to take over his life.

But there are others who want inside the actor -- permanently -- including Diaz (now obsessed with having Keener to herself) and the boss in Cusack's office, who it turns out knew about the portal all along and has been using it to hop from body to body as a form of surrogate immortality.

Spike Jonze -- who cut his teeth on innovative TV spots (Levi's "Tainted Love" spoof of "ER") and music videos (Weezer's "Buddy Holly") -- deftly navigates the abundant irony and symbolism in "Being John Malkovich" to mold a crafty, one-of-a-kind film that is at once uncanny and sublimely side-splitting.

I'm dying to tell you more, but if I don't shut up I just know I'll give away everything and I don't want to spoil it. Destined for well-deserved cult status along side such creepy-comedy masterpieces as "Brazil" and "Harold and Maude," "Being John Malkovich" is one of those brilliant movies that's best discovered with its curious surprises intact.