Mystery still No. 1. CONTINUING LAST FRIDAY'S PULLOUT

May 9, 1988

DOGEARED pages confirm what any children's librarian will tell you: Mysteries continue to be the favorites among their regular book borrowers. Several new titles should be in steady circulation this season as youngsters gravitate to favorite reading spots.

The Treasure of Plunderell Manor, by Bruce Clements (Farrar Straus & Giroux, New York, $12.95, 180 pp., ages 12 and up), is a Victorian thriller reminiscent of last year's winning ``The Ruby in the Smoke,'' by Philip Pullman (Knopf, New York). It not only stars an unusually bright and likable leading lady, but also is a fine spoof of period melodramas.

The nonstop action begins when 14-year-old Laurel Bybank, an Irish orphan, becomes lady's maid to 17-year-old Alice Plunderell - also orphaned and kept locked in her tower room by a devious uncle and aunt, the Lord and Lady Stayne.

The two girls are left to die in an abandoned monastery one wintry night while the greedy relatives go in search of a treasure chest that Alice's father buried somewhere on the manor property. But Laurel saves the day and makes good their escape and eventual homecoming.

Although the author plays his characters off each other - the resourceful, independent, and plucky Laurel helping the somewhat snivelly Alice - it's all in good fun, and readers will appreciate the pokes he takes at gender roles.

Alice may be lady of the manor, but Laurel is the real heroine. She knows when to hold her tongue and when to stick it out.

She is also perceptive enough to realize that her future lies in America, not in the arms of the young man who seeks her hand in marriage. Hopefully, author Clements is plotting a sequel for Laurel in the New World.

Manor houses and Victorian England likewise set the spooky scene in Moondial, by Helen Cresswell (Macmillan, New York, $13.95, 202 pp., ages 10 and up), a compelling time-travel fantasy that's strong on evocative moods and rich narrative.

The very contemporary Minty Kane, complete with cassettes and headphones, is sent to her Aunt Mary's for the summer holidays in the rural village of Belton, site of a National Trust House that's a centuries-old prison to several young children.

Minty discovers their plight through her ``sixth sense'' ability to feel presences down through the ages, and she is determined to help them escape the prejudices and injustices of their eras.

At the same time, Minty is doing all that she can to help her comatose mother, who appears to be similarly ``lost in time'' as the result of an automobile accident, and the interplay between the two ``rescue'' subplots is convincing.

The Latin motto on the old sundial that transports Minty between the centuries - ``Light and Shadow by turns, but always Love'' - becomes her guiding light for the present, as she learns that love can indeed conquer all fears.

Author Cresswell displays the same imaginative powers that have won her loyal readers for her ``Bagthorpes'' series, and draws fresh drafts from timeless British storytelling traditions. American readers shouldn't have any trouble negotiating their way around references to ``torches'' and ``tea caddies.''

In The Freshman Detective Blues, by P.J. Petersen (Delacorte, New York, $14.95, 205 pp., ages 10 and up), the scene shifts to northern California and a decade-old murder mystery. Fourteen-year-old Eddie and his 17-year-old buddy, Jack, pick up extra money scavenging fishing lures, poles, and anchors from the shores of Muir Lake, where Eddie's family runs the Grizzly Creek Marina.

As the water drops to an all-time low because of a continuing drought, the boys come upon a skeleton tied to a rusted boat motor. They spend the rest of the book trying to identify the skeleton and figure out who put it there - and why.

The audience for Ride a Dark Horse, by Lynn Hall (Morrow, New York, $11.75, 176 pp., ages 12 and up), is probably limited to young girls who grew up playing with My Little Pony and now have their sights set on horseback-riding lessons.

It's unfortunate, because this is a convincing mystery that ought to attract a wider readership.

As an exercise rider at Tradition Farm in southern Ohio, 17-year-old Augusta (Gusty) McCaw has an enviable job and life style - until she's abruptly fired one day for selling information about the stable's thoroughbred pacers.