Shakespeare's Twelfth Night is a comedy that refuses to take anyone seriously. That the characters take themselves seriously is what makes them so funny — in a sad way. At the Pennsylvania Shakespeare Festival, director Matt Pfeiffer uses the striking scenic and lighting design of Steve TenEyck to create a show that mixes riotous laughter with a sense of the tragic.

The core event: Shipwrecked on the imaginary isle of Illyria, Viola cross-dresses as boy page Cesario to enter the service of Duke Orsino. This initiates an absurd, gender-bender love triangle between Cesario, Orsino and Olivia that does not clear up until the end.

Young Victoria Janicki is affecting as Viola/Cesario, full of double entendre and vibrantly present. Yet Viola falls in love with self-absorbed Orsino (Akeem Davis). You also have high hopes for Eleanor Handley's Olivia, a wonderfully imperious countess. But Olivia also proves flighty in her infatuation for Cesario.

And we are just getting started. In addition to fanciful lovers, Twelfth Night is full of manically comic subplots. Pranksters Sir Toby Belch (Scott Greer), Sir Andrew Aguecheck (Alex Bechtel), and Maria (Suzanne O'Donnell) torment Malvolio (Greg Wood), a puritanical social climber. Thanks to the wild costume design of Olivera Gajic, everyone is more ridiculous.

Alex Bechtel composes an original score that echoes Orsino's opening line, "If music be the food of love, play on." Just as Cupid fires off arrows willy-nilly, Bechtel's music has matching caprice. A small combo — piano, guitar, accordion and drum — pops up to underscore the lovers' whimsy.

Just as unpredictable are the mercurial appearances of Feste, the clown (Eric Hissom). Surely Shakespeare's editorial voice, Feste plays guitar and sings for money with a melancholy air. Hissom has perfect comic timing. His Feste is also sadly distant but never disdainful, as even disdain admits to emotional involvement.

The PSF show is full of hilarity. When Malvolio discovers a forged letter, Wood's portrayal is so endearingly funny it defangs the sadistic malice of the plotters. And both Wood and Hissom break the fourth wall to engage the audience, a tactic that usually falls flat but works perfectly here. Twelfth Night even has a happy ending.

At the same time, Twelfth Night ushers in the despair of late Shakespeare. Except for Feste, no one is sane. Shakespeare turns the comic device of mistaken identity into a metaphor for human frailty. Class and sexual identities are in flux. With his long parade of fools, Shakespeare achieves the comedy equivalent of a problem play. Here, he argues: The human being is a lost soul.