Sherlock Holmes fans who may have been worrying about the reputation of their hero-remember his portrayal as an angstridden druggie a few years back in "The Seven Per Cent Solution"?-can breathe easy. In "Murder by Decree," the latest attempt by screenwriters to improve on Sir Arthur Conan Doyle's imagination, the legendary detective returns to the screen alert, sober and eminently sane.

But diehard fans may have just as hard a time getting used to the new, improved version, for as Christopher Plummer plays him, Holmes is-gasp!-human. He's not afraid to laugh or show affection or, on one remarkable (for Holmes) occasion, cry. Plummer's interpretation is a real departure from the imperious image we've come to expect over the years.

In this case, though, the gamble pays off. A backslapping Holmes would be an affront, and it's a testimony to Plummer's adroitness as an actor that he brings humor and humanity to the part without sacrificing the air of aloofness so crucial to Holmes' appeal.

As loyal sidekick Dr. Watson, James Mason has done some legend-tampering of his own, with the same believable results. Instead of a thick, plodding caricature, we get a droll, intelligent partner worthy of Holmes' association.

What a team! Plummer and Mason are a delight. There's genuine affection in their relationship, and an easy camaraderie that's a pleasure to watch.

The story itself is, well, elementary. It's a sort of docu-drama in reverse: Instead of inventing a story line to fit a real person, the writers have placed the fictional Holmes on the trail of the real-life murderer Jack the Ripper, who terrorized London prostitutes in the 1880s. It's grippingly acted out, but the solution won't come as a surprise to anyone up on the latest Ripper theories.

As in the books, a large part of the movie's appeal is the window on Victorian society. Glimmers of the lives of East End prostitutes and insane-asylum inmates are especially poignant. The filmmakers here are as much concerned with the authentic recreation of period detail as they are with plot and characterization, and the result is a stunning depiction of 19th-century London. The movie is so visually rich, in fact, that at times it's self-defeating; you might miss a clue of two while admiring a lush Victorian drawing room or a well-done pea-soup fog.

Those who are not inured to the excessive violence that is commonplace in movies today should be forewarned that "Murder by Decree" is a graphically gory as the best, or worst, of them. In this case, though, the movie is saved by the literate script, capable actors and meticulous attention to historical detail.

Sir Arthur would have approved.