It may not be as suspenseful as Hitchcock or as trendy as Jessica Fletcher, but this Sherlock Holmes adventure - based loosely on Sir Arthur Conan Doyle's "The Sign of the Four" - is still a jolly good mystery.

Younger audiences, accustomed to Hollywood's penchant for high-speed thrills and high-tech excitement, may have some difficulty getting into the deliberate, slower pace of this very British yarn.In the hands of an amateur troupe "The Crucifer of Blood" could end up looking as ridiculous and stilted as an old-fashioned Saturday matinee serial. But Pioneer Theatre Company gives Paul Giovanni's script the kind of professional spit-and-polish that would make a British soldier proud.

The production values - from the superb cast to George Maxwell's splendid scenery - are first-rate from top to bottom.

Sherlock Holmes and his stalwart sidekick, Dr. John Watson (Jim Jansen and William Langan) sleuth about London, chasing after clues to a mysterious and deadly blood oath and a treasure chest filled with a maharaja's stolen jewels, both of which suddenly surface 30 years after the pact was signed by three British troopers at a fort in India. There are more twists, turns and dead ends than you'd find in an English garden maze.

The plot, beginning with a prologue set in 1857 inside one of the 100 gates of the Red Fort at Agra, India, then shifting to the legendary Holmes' library at 221-B Baker Street exactly 30 years later, takes the audience on a two-night journey to retired Major Ross' Pondicherry Lodge at Maidenhead . . . the eerie Gate of a Hundred Sorrows opium den in London's notorious Limehouse district . . . and two boats on the River Thames.

I won't give away too much of the plot here. That would ruin the fascination of watching Holmes study the clues and reach his carefully thought-out deductions.

When you're not savoring George Maxwell's sets, James Prigmore's dramatic musical underscoring, Carol Wells-Day's costumes, Peter L. Willardson's lighting and Cynthia McCourt's hair designs and make-up, there are several finely honed performances to enjoy.

Fight director David Boushey and, of course, guest-director John Goings also deserve a round of applause.

Jansen, who gave PTC patrons a delightful performance as another famous Briton a couple of seasons back (Professor Henry Higgins in "My Fair Lady") is perfectly cast as Britain's most famous detective. Always itching to pursue yet another case, Holmes' solution to being frustrated is a shot of his own seven and one-half percent . . . of cocaine. But once the game is afoot, Holmes plunges right in - making Inspector Lestrade (Julian Gamble) of Scotland Yard look like a fool and uncovering clues right and left while the body count slowly climbs.

The sleuthing begins in earnest when distraught Irene St. Clair (Valerie Leonard) seeks Holmes and Watson's help. Is she a frightened little mouse or a conniving rat?

Max Robinson has a theatrical field day in the role of sinister Major Ross. He ages 30 years between the Prologue and Act One, then has to change back into the younger Ross for a sequence in the nightmarish opium den where former comrade and blood-pact colleague (Capt. Neville St. Claire - Irene's opium-addicted father) hallucinates and interacts with Ross' ghost.

Claywood Sempliner portrays Capt. St. Claire, a decrepit man who meets a grotesque and wretched demise.

Others in the cast include Sam Stewart as the mysterious and vengeful Jonathan Small, Rick Frederick as Ross' entrapped houseboy, Birdy Johnson, and David Val-enza, Jason Ball, Mearle Marsh, Javier Cordoba and George Spelvin in a variety of secondary roles.

- Sensitivity rating: Some fairly graphic violence and drug abuse (both Holmes' shooting cocaine and the opium den).