Whodunnit? The University of Minnesota Showboat Players dunnit, with Agatha Christie's period thriller, The Mousetrap, on the Victorian-styled Minnesota Centennial Showboat, with the stylishness of professional summer stock theater.

No hack players, these. They act, speak in credible English accents, sing and dance, as though they have trod the boards for years. The one clue to the fact that they are a university troupe is their youth.

They embrace the old chestnut of the The Mousetrap under director Kenneth Noel Mitchell with zest and a nicely contained sense of tongue-in-cheek fun. With Agatha Christie's cardboard-cut-out English types, the play could lend itself to the campy comedy of melodrama. The Players pay a nod to melodrama, with Martin Gwinup's creepy sound effects and Jean Montgomery's stagey lighting, but they play it as a mystery thriller and still find laughter.

The action takes place in Monkswell Manor, an old house just outside London in 1948. Young Mollie and Giles Ralston (Alison Mary Forbes and Jack Matheson) have opened it as a hotel. On a dark and snowy night, as they await their first guests, Mollie learns from the radio of a murder in London. The expected guests arrive, plus a mysterious unexpected guest, and snow closes the road. A policeman turns up on skis, announcing that Monkswell Manor was implicated in the London murder and that the eight people, trapped together in the old house, are at risk of being murdered. Sure enough, a throat gets throttled. Who will be next ... dum de dum-dum, da?

In the tradition of Mississippi riverboat theater that was designed to entertain travelers as they steamed up and down the Mississippi, the Showboat Players interweave olios between scenes. Olios are amusing song and dance routines that are flamboyantly costumed and bear little relation to the play on stage. Vern Sutton directs the olios with palpable dash. I found them a distraction from the main story at first, but I succumbed to their sheer verve and nonsense. Samuel Ellingson's olio costumes are a work of art in their own right.

In true ensemble playing, young Emily Brooke Hanson dodders in an embellished portrayal of old age as the tart Mrs. Boyle, while Michael Rasmussen resorts to a gray wig and moustache as the mature Major Metcalf. Nicholas Harazin is winning as the over-the-top Christopher Wren. Megan Bartle shines as Miss Casewell, an urbane, cigarette holder wielding modern young woman in the manner of Dietrich, and Jonas Goslow plays the mysterious Mr. Paravacini as a sort of Count Dracula knock-off. Fresh-faced Ryan West makes a boyish Detective Sergeant Trotter, and Susan Hsu accompanies the action with an off-stage piano, just as riverboat theater might have been accompanied in the past.

Matt LeFebvre's detailed period set of the faintly shabby living room in Monkswell Manor has all the requisites for mystery thriller fun - six doors to facilitate multiple comings and goings, heavy curtains to hide behind, a window that can be hopped through in a hurry-well, you get the idea.

To get a playful mood going before the play and again after the interval, three ensemble members rev up the audience in interactive repartee. The olios between scenes make for a longish production, but it's lighthearted summer fun played by a group of talented young performers aboard a moored replica of an 1858 stern-wheeler paddle boat.

The Mousetrap June 18 - August 28, 2004. Tuesdays - Saturdays 8:00 p.m. Matinees 2:30 p.m. Tuesdays, Thursdays and Saturdays. $10 -$20. Minnesota Centennial Showboat, Harriet Island, downtown St. Paul. (On board dinner available before the show.) Tickets: 651-227-1100. Toll Free 800-543-3908. www.showboattheater.com.

- Elizabeth Weir