Dip one little toe into "Echoes in the Darkness" and you find yourself slipping in all the way, body and soul. It isn't just an altogether superior, completely gripping docudrama, it's a virtual vortex.

A two-part, five-hour CBS movie airing tonight at 9 and Monday night at 8 on Channel 9, "Echoes in the Darkness" belongs to but transcends a familiar genre, the TV movie about a horrendous crime and the apprehension and trial of its perpetrators. Even after "Fatal Vision" (mentioned during a trial scene in Part 2) and "The Burning Bed" and the others, "Echoes" comes as something of a mordant revelation.

It is probably the best film of this kind ever made for television. One reason is that though the crimes involved are indeed horrendous, the story is told more in sorrow than in anger, and with a distinct literary flair. The storyteller is the gifted Joseph Wambaugh, who adapted his own book for television.

As skillfully and painstakingly directed by Glenn Jordan, "Echoes in the Darkness" traces the convoluted and confounding history of the infamous Main Line murder case in Pennsylvania and of police and FBI efforts to solve it. It was, says the prologue, "one of the most massive homicide investigations in American history."

Part 1 details the background of the crime and, in the process, offers a devastating portrait of academia and its privileged, sometimes suffocating isolation. Eccentricities are cherished here, and superciliousness runs rampant. Bill Bradfield, a teacher and would-be poet played by Peter Coyote, is a megalomaniac and a dilettante who surrounds himself with friends who are his virtual subjects.

He's like the most dreaded sort of Hollywood star, in a way, and Coyote's portrayal is meticulous to a fault, or to all the faults tied up in this one manipulative sociopath, as he is later described. Bradfield is a man given to such pronouncements as "I have no need whatever for a sexual relationship with anyone" and an obsessive fondness for traitorous poet Ezra Pound. Lying on a beach with members of his enfeebled inner circle, he suddenly pops up and says to one of them, "Vince, Vince, I need to go to a church. Take me to a church!"

His entourage includes the adoring and doomed Susan Reinert, played to touchingly neurotic perfection by Stockard Channing, and his longtime house-mate Sue Myers, played attentively and poignantly by Cindy Pickett. Channing and Pickett, with Wambaugh's help, allow an outsider to understand why these women would remain bound to a man so obviously wrong for both of them.

There is the implication that Bradfield was a kind of omnisexual; he seems to be trying to seduce everyone within his sphere, though it is implied that some of the relationships, however intense, were platonic. Such appears to be the case with the aforementioned Vince, a fellow instructor and professed celibate played by the compellingly intuitive young actor Zeljko Ivanek, who in Part 2 tells the FBI, "I don't want to be killed. I just want to teach English."

Another colleague, Chris, played by Alex Hyde-White, is enlisted by Bradfield for such chores as a late-night session of rubbing fingerprints off $25,000 in cash early in the conspiracy.

Wambaugh plunges you into a grotesque communal madness almost at once, first with an unexplained 1978 robbery that for a long time appears to have no relationship to the rest of the story, then with his introduction of Bradfield and the peculiar world he dominates. Peripherally, or so it seems, that world includes the imperious Jay Smith, principal of the high school in Upper Merion Township where Bradfield teaches.

As played with unnerving zeal by versatile Robert Loggia, brilliant in the part, Smith is a study in devious duplicity, an officious pedant who dictates announcements over the school's public address system while striding around his office in his underpants. Soon comes the night when he is stopped by traffic cops who discover a cache of guns in his car and, at his home, gallons of stolen nitric acid and porno books with titles like "Her Canine Lover."

So bizarre are the characters that they could have been torn out of the scenario for the weirdo chiller "Blue Velvet" or one of the theatrical concoctions of Joe Orton. Peter Boyle, who materializes in Part 2 as the past-his-prime state policeman in charge of investigating the crime, says of this lavishly educated crowd, "There ain't one of 'em got enough sense to tell a cat drop from a candy kiss."

He does have a way with words.

The film is not just about strange people, of course, but about murderous ones. Wambaugh ravels his way to the grisly crime, committed near the conclusion of Part 1, then unravels the seven-year investigation in Part 2. His script is a marvel of scrupulous craftsmanship, but it is more than that. It has a profound sense of lament for the coldness of the killings and for the fact that the motive appears merely to have been money: $730,000.

For this a woman is viciously murdered and so, apparently, are her two children (whose bodies were not found, according to the film). Wambaugh is able to weave his admiring narrative about the rigors and pitfalls of police work and also sustain a pervasive sense of tragedy. The murdered woman is not portrayed very sympathetically, but a speech by an FBI man on courthouse steps in Part 2 puts the magnitude of her suffering in chilling perspective.

No one, he convincingly tells a cop, deserves to die so ignobly. Wambaugh covers all the bases, and if the number of details sometimes seems excessive, they contribute to an impression of dogged authenticity. The mixed bag of crucial clues include a copy of Penthouse magazine, fibers in a carpet, a misplaced comb, a sudden hailstorm, a hatchback left open in a Harrisburg parking lot and, key to the prosecution, a little green pin with the letter "P" printed on it.

Treat Williams joins the film well into Part 2 as a deputy attorney general assigned to the case years after it has begun. Williams says of Smith, whose cold eyes he catches in court, "He looks as banal as Adolf Eichmann." In the character of Bradfield, one can see dark echoes indeed, of Charles Manson and Jim Jones and sundry latter-day Rasputins.

One principal member of the investigative team dies before the case is solved, but boyish Gary Cole (the homicidal doctor in "Fatal Vision"), as Trooper Jack Holtz, is there from beginning to end, and reassuringly so. Some key questions apparently were never answered, but viewers who stay with the film will feel the satisfaction of justice being done -- by judges, juries and the persistent Wambaugh.

Although it is a film that deals with unspeakable acts of violence, "Echoes" contains no violence itself. None. There are no on-camera reenactments of the crimes, no lurid flashbacks to the doing of dirty deeds -- the cliche's of the genre. This is a sign of integrity. And the film needs none of that to hold one's attention tightly, something it does to the very, very, end.

Wambaugh's last word on the case has little to do with the victories of the prosecutors or of the investigators who tracked it for seven long years. It has to do with remembrance of the victims. To call a new TV movie -- maybe any kind of movie -- "unforgettable" is to risk being premature, but if ever one stood a chance, "Echoes in the Darkness" does.