‘Gallowglass’ Serves ‘Mystery!’ Well : TV review: Although no masterpiece in itself, the taut three-part drama remains superior for its tension and deft execution.

British whodunits continue to flourish on PBS, where ever-seductive “Mystery!” opens its 16th season tonight with “Gallowglass,” another rendering of a novel by Ruth Rendell writing under her Barbara Vine pseudonym.

This is an encore for Rendell as Vine. The BBC’s stunning version of Vine’s “A Dark Adapted Eye”--a whydunit that drizzled thick murkiness over a woman’s bloody murder of the younger sister she adored--launched “Mystery!” in 1994 and, along with “Gallowglass,” is slotted to be rerun next summer.

“Gallowglass” is no “A Dark Adapted Eye.” Nor is it “Prime Suspect,” Granada Television’s trio of scintillating three-parters about Helen Mirren’s British copper, Jane Tennison, a flawed heroine who lit up “Mystery!” in past seasons.

Of course, “Prime Suspect” will not quite be “Prime Suspect” itself when returning to PBS on Oct. 22 after a one-season absence. Reshaped by Granada as three independent two-hour stories instead of as a serial, “Prime Suspect” is being chauffeured uptown to “Masterpiece Theatre,” a symbolic promotion that affirms its elite status while also instantly energizing a frayed and yellowing PBS signature series that long ago used up its masterpieces and has edged toward mediocrity in the 1990s.

Although hardly a masterpiece itself, the three-part “Gallowglass” is definitely superior, well-acted, deftly executed, rewarding television, its gnarled characters suspensefully winding their way through a curvy plot threaded by madness, obsession, kinkiness and sexual tension. In other words, not exactly a ringer for “Murder, She Wrote.”

An ancient Gaelic word meaning servant to a chieftain, gallowglass in Vine’s story refers both to Joe (Michael Sheen), a former mental patient who worships and is dominated by a mysterious young man named Sandor (Paul Rhys), and Paul (John McArdle), who takes a job as driver-bodyguard to Nina (Arkie Whitely), a striking former model and wife of a moneybags who fears for her safety. These seemingly unrelated stories ultimately converge, creating conflict and psychological tautness.

Later, Joe’s pushy sister, Tilly (Claire Hackett), joins him and Sandor, who obviously has something unpleasant in mind for Nina--an agenda that Jacqueline Holborough’s script tantalizingly clouds over until well into the second episode.

“Gallowglass” is driven largely by Rhys’ seething energy as the dangerous Sandor, with support from Sheen’s slothful, spineless Joe. Even they cannot adrenalize a laborious section of Part 3 that stalls the story, but director Tim Fywell (“A Dark Adapted Eye”) gets it all together in time for a multiple-twist ending that is interestingly complex if not entirely logical.

* “Gallowglass” airs at 9 tonight on KCET-TV Channel 28.