"Toyer" is a new psychological mystery play that emits a thin, steady film of uncleanliness, rather like a corroded exhaust pipe. Audiences who head into the Eisenhower Theater with expectations of mounting suspense will depart a scant hour and 45 minutes later with an urge to shower.

In the lexicon of playwright Gardner McKay, the "toyer" is a criminal who toys with his victims--all beautiful young women--before lobotomizing them and transforming them into beautiful young vegetables. By the start of the play, which opened a six-week run Saturday night, he's chalked up enough lobotomies to become the most successful mass murderer "in West L.A. history" and every single woman with a brain is in a state of terror.

With that as the background, McKay has written a two-character cat-and-mouse game that involves Maude (Kathleen Turner), a leggy, tennis-playing therapist who lives in a house tucked away in a remote L.A. canyon, and Peter (Brad Davis), the slicked-back motorcyclist who helps start her stalled Volkswagen one night, follows her home and then behaves most oddly. Is he the Toyer? And if so, is she going to wind up on the front pages of the world's newspapers just like all her predecessors?

"Toyer" really doesn't have a plot. Rather, it is built on a succession of flip-flops that may or may not catch you unaware. One minute you're supposed to believe it's the Toyer up there. The next, McKay will pull a switch and you're not so certain. Since Maude has recently been pestered by a voyeur, who not only took pictures of her dressing but trampled her geraniums, it is entirely possible that Peter is simply the wielder of a candid camera, not a lethal knife. Then, too, Peter has a fair number of fanciful explanations as to who he really is. So who's to say? You may also well ask, who's to care?

Director Tony Richardson clearly sees it all as a variation on a sporting match. The plunk/plunk of tennis balls being batted back and forth is the leitmotif of the evening. His staging has a perverse sheen, but it's also patently manipulative in the way that it dances cozily around the old taboos, never meeting them head-on. One of my female acquaintances said at intermission that the whole affair made her feel "squirmy." I don't think she was just reacting to the subject matter, but to the ambivalence of a production that wants both to tantalize and terrorize us with the same material. At one point, Turner is made to strip to the waist before a full-length bathroom mirror and fondle herself. Davis plays much of the second act in his briefs. Rubber gloves and knives are prominently employed. To call it pornography, however, is to grant it a vigor it doesn't have.

If "Toyer" hummed with high-wire tension, maybe it would seem somewhat less sleazy. But it manages only a few mild surprises and, since neither character is likely to claim your allegiance, the ending offers few satisfactions. Both Davis and Turner are "hot" performers on a movie screen, but they do not bring a great deal of incandescence to the stage. To begin with, she is taller than he, so I wasn't completely convinced that in a pinch she couldn't gain the upper hand. But mostly she seemed to me to be a woman stunningly lacking in simple common sense.

Davis has the chameleon role, although not a chameleon's gifts. If the play is to work at all, the character must convince us alternately that he is boyishly charming and dangerously psychotic, innocent as a booty and guilty as a noose. Davis, short on the charm, has so far mastered only an open-mouthed form of retarded development.

McKay's script does try to strike a few philosophical notes along the way--things to do with violence, society, the press and individual responsibility. But I wouldn't let that fool you. "Toyer" is the theatrical equivalent of an exploitation film. The ultimate "toyees" are those of us sitting patiently out front, wondering, not unlike the heroine, how we landed in this unsavory stew.

TOYER. By Gardner McKay. Directed by Tony Richardson; set, Rouben Ter-Arutunian; lighting, Martin Aronstein. With Brad Davis and Kathleen Turner. At the Eisenhower Theater through March 5.