As he slouches into middle age, cigarette and drink in hand, Steve has just been dumped via e-mail by his boyfriend of eight years. His playwriting career is a dying echo of what it once was, and his Brooklyn apartment looks like he stopped decorating sometime in the mid-’90s.

Depressed, intensely lonely, creatively and romantically desperate, Steve has approximately one thing going for him: a drop-dead view of the Manhattan Bridge out his living room window. Until, that is, Idi Amin bursts through that window, laughing like the Ghost of Christmas Present.

The broken glass will be taped over with what appear to be trash bags; Steve’s psyche is another story. The former dictator of Uganda, an otherwise surprisingly affable hallucination, has come to demand that Steve write him a play, the story of Amin’s life. “You will do this in three days,” Idi tells Steve, “or if not, by this hand, you will die.”

Such is the premise of David Grimm’s “Steve & Idi,” a buoyant, highly theatrical, and unwieldy comedy receiving its world premiere at Rattlestick Playwrights Theater. That Mr. Grimm — who, his bio notes, last acted onstage 18 years ago — takes the role of Steve suggests the closeness to his heart of this play.

That proximity may be part of the reason for his insufficient pruning of the script’s considerable overgrowth: a scene, for example, that’s more prosaic debate — about writing, about politics, about plays being workshopped to death — than dramatic conversation. That such flaws don’t obscure the worthy play that lies beneath is thanks to the sure hand of director Eleanor Holdridge and an ebullient performance by Evan Parke, who rips into the role of Idi like a ravenous carnivore into thick, juicy flesh. Mr. Parke’s Idi is a crude, violent, egomaniacal charmer, larger than life and fully three-dimensional.

Anyone who is old enough to get the joke of the title — a reference to the husband-and-wife singing duo of Steve Lawrence and Eydie Gormé, stars back when Johnny Carson was a brash young thing — is probably also old enough to remember the brutal and showboating Idi Amin, who died in 2003. The dictator ruled Uganda in the 1970s and killed hundreds of thousands of his people, including one of his own wives.

Not a figure ripe for hilarity? So you’d think. The Krispy Kreme-loving Idi of Mr. Grimm’s creation, however, very much is.

Like any good subject of a writer’s work, Idi moves in with Steve. He hogs the couch, wears Steve’s bathrobe, fires up his bong. Idi quickly becomes inescapable, imposing his point of view, his voice, his every thought on his host. And yet, to a heartbroken man, Idi Amin is a gift as a houseguest.

“Make me to be remembered and I can make you to forget,” he tells Steve.

Although it is deep in Act 1 before Idi makes his appearance, he brings with him Mr. Grimm’s true subject, the one on which he speaks most eloquently: the obsessiveness of the writer’s life, and the damage and the healing that can come from full immersion in that work. In Idi Amin, personification of the ugly, the terrifying, and the unfamiliar, Steve locates, somehow, the depths of his own soul.

Mr. Grimm’s work has been produced at the Public Theater (“Kit Marlowe” in 2000, “Measure for Pleasure” in 2006) and at some of the nation’s most prominent regional theaters, so it is surprising to find this play getting its world premiere at the 99-seat Rattlestick. In that context, Steve’s disappointment and rage about the state of the theater, like his anxiety about the success of younger playwrights, gain a certain resonance. And yet the play is a palpable expression of love for the theater.

Toward the end of “Steve & Idi” is a scene in which Mr. Grimm is onstage alone with a sock puppet — which is to say, onstage alone. Theater doesn’t get simpler than a sock puppet. But when the chemistry between an actor and a talking hand works, as it does here, it utterly enchants.

Until May 24 (224 Waverly Place, between Perry and West 11th streets), 212-868-4444.