A schoolboy has encountered a ghost in Hempstead Heath -- one dressed, he says, "all in white, as a ghost should be." Is it in fact an emissary from eternity, or merely an escaped lunatic? The question is one of many to be answered -- in due time -- by "The Woman in White," a five-part Mobil "Mystery!" presentation that starts tonight at 9 on Channel 26 and other public television stations.

Set in 1849 and based on the antique and precedent-setting mystery novel by Wilkie Collins, "Woman in White" offers up by the oodle all those things loyal fans of the genre savor: exquisite Victorian trappings, mysterious doings (and doers of them) on the moors, duplicities, felicities and the atmospheric clopclopclop of horse's hooves on cobblestone as a carriage is drawn up to Limmeridge House, where there's such a lot of lurkin' to do.

Daniel Gerroll is the attractively colorless hero, Walter Hartright, and Diana Quick, who was Julia in "Brideshead Revisited," is the pluckily resourceful Marian, who speaks in neatly diagrammed sentences and utters such self-disparaging observations as "I am inaccurate, as women usually are." Heaven forfend that such a creature would ever enter the newspaper game.

Where there's a will, there's a wisp, and in part one we are flirted with by an alleged spectral apparition but more likely to be entranced with the character of Frederick Fairlie, played with elegant foppish severity by Ian Richardson. Frederick sits in his study in a state of imperiled tranquility. "I am such a sufferer," he declares, imploring Hartright, "Gently with the curtains please; the slightest noise from them goes through me like a knife."

Too bad he didn't live to see the Age of Anxiety. He is but one of many deftly stirred ingredients that helps make "Woman in White" not merely rather tasty, but devilishly yummy.