"Blithe Spirit," Noel Coward's season-appropriate confection about a marriage gone spookily south, is as weightless as Halloween itself: Early mentions of a seance, a dead first wife and the current spouse's declaration that she "never for an instant felt the least bit jealous" of the deceased are all you need to hear to know where this is going.

The play, staged by the Olney Theatre Center, traffics in Coward's usual milieu: upper-crust Britain. Complacent couple Charles (Paul DeBoy) and Ruth (Julie-Ann Elliott), dry martinis in hand, are awaiting the arrival of a medium, Madame Arcati (Halo Wines). Charles, who is writing a novel about a psychic, has invited her to their home for research purposes. Neither takes seriously the somewhat batty Arcati, who shows up on a bicycle with her loud dress tucked between her legs and proceeds to flit about their well-appointed home to establish a connection with the dead.

Charles, however, is soon made a believer. After the table-wobbling seance is over and Arcati goes home, a new guest appears: Elvira (Kate Goehring), Charles's "physically triumphant" and playful first wife, who died while they were married. Only Charles can see Elvira, and though he insists he didn't summon her, she can't leave without Arcati's assistance. Which is fine by Charles, who, to Ruth's great irritation, begins to enjoy the still-sprightly Elvira's company and his new role as an "astral bigamist."

Unfortunately, the liveliest character in "Blithe Spirit" is the one who's dead, which makes the comedy drag a bit whenever Goehring, looking appropriately ethereal in shimmering shades of white gold, is offstage. Her Elvira is pouty and passionate, in contrast to the measured and controlling Ruth, to whom Charles soon complains, "You don't even allow me to have a hallucination if I want to!"

Despite the Olney cast's nimble handling of Coward's sophisticated and frequently witty language, the plot's too thin to be spread over nearly 21/2 hours. Gags such as a frantic maid (Tara Giordano) or the mixed-up conversations between the living and the dead lose potency after their third or fourth repetition, and the labored setup in which Ruth and Charles dissect their staid marriage at length makes the subsequent ringing of a doorbell one of the play's more welcome moments.

Act 2 moves much more briskly, with a sinister plot turn and a tricked-out ending that rattles James Wolk's gorgeous, intricately decorated living- and dining-room set. Credit should also go to lighting designer Robert Jared, whose blue-purple dusks add coziness and whose bright mornings are appropriately crisp. Happily, the thoroughness of Olney's presentation of "Blithe Spirit" helps make up for the occasional tedium of Coward's script.

Blithe Spirit, by Noel Coward. Directed by John Going. Costumes, Howard Tsvi Kaplan; sound, Chas Marsh; lighting, Robert Jared; set, James Wolk. Approximately 2 hours 35 minutes. Through Nov. 7 at Olney Theatre Center, 2001 Olney-Sandy Spring Rd., Olney. Call 301-924-3400 or visit www.olneytheatre.org.

Julie-Ann Elliott as Ruth, Paul DeBoy as Charles, and Kate Goehring as the gregarious ghost Elvira, Charles's first wife, in Olney Theatre Center's "Blithe Spirit."