Who knew "Cymbeline" had so many references to the heavens? On opening night, every one seemed to allude to the skies above Mellon Park, which entered the action on cue, saving their grandest pyrotechnics for the arrival of sky-born Jupiter and subsequent battle scenes, calming down just in time for the post-traumatic rebirth and sweet revelations.

You can't always count on weather to provide such splendid special effects. But every distant police siren seemed to fit in, as well. Performing outdoors, whatever happens adds zest to the feast -- this being Shakespeare, who throws a wide metaphoric net, and Quantum Theatre, which thrives on planned serendipity.

But who knows anything about "Cymbeline," period? Even experienced Bard-goers rarely see it staged. So the great achievement of director Karla Boos' lively, energetic, visually striking condensation is how clearly it tells a complex story.

Complex but fun. Although "Cymbeline" is generally classed as a late Romance, like "A Winter's Tale" and "The Tempest," Boos and company play it convincingly as comic melodrama, with vague affinities on the silly side to "Doctor Who" or Monty Python.

The setting is pre-Christian, early-Roman Britain, about which Shakespeare didn't know very much, so he's freer to invent. Cymbeline, King of the Britons, turns both rebellious son and tyrannous father, denying tribute to fatherly Rome and exiling Leonatus, the man his daughter, Imogen, has married.

He and his new Queen, deliciously played by Mark Staley a la the evil queen in "Snow White," intend Imogen for her comic clodpole son, Cloten. Meanwhile, in exile in Rome, Leonatus places a deadly wager with slimy Iachimo on his wife's chastity.

Catastrophe ensues. Imogen flees the court, disguised as a boy, to take refuge in Wales with three other fugitives. She dies -- or does she? The Romans invade. Someone gets his head cut off, but who? And then things get really snarled up, before a bravura final scene of multiple happy endings.

But it's the telling that entertains most. First, there's the setting. The audience is wrapped around a thrust stage framed by tall cypresses, with a distant view of lawn and stone lions, very Arcadian. Susan Tsu's costumes are cool and flowing, both antique and futuristic, and C. Todd Brown provides lovely lighting effects (including props), even without the possible assist of the heavens.

Second, there's the casting, in which Boos contrives to use just one woman and six men to play 20-some characters. There's genius in the pairing of each actor's major roles. To his gloating Queen, Staley adds the other villain, the conniving Iachimo. David Whalen plays both King and Roman commander, plus the ultimate chieftain, Jupiter, and throws in a comic jailer for good measure.

Sam Turich doubles the headstrong young hero, Leonatus, and his comic-villain mirror image, Cloten. (For once, Imogen's mistaking the body of one for the other makes perfect sense.) Patrick Jordan has a subtler pairing: servant Pisanio and fugitive prince, both loyal, one goofier than the other.

Rick Kemp and Joel Ripka add a handful of roles each. Kemp is a rock, especially impressive as the older fugitive, and Ripka has a fine and clarifying turn as a composite character (doctor, soothsayer and maybe more).

Mikelle Johnson plays just Imogen, but she disguises herself as Fidele, so she gets a second role, too. She starts the play seeming ill at ease, her voice forccd and hard to hear, but as Imogen reacts to adversity with invention and spunk, Johnson begins to shine, bringing a goofy comedy more appealing than wounded rectitude.

The pervasive doubling points up Shakespeare's contrasts and parallels and often provides robust humor, as when one actor has to interact with himself. Tsu's costumes help, a swirl of scarf or velcro'd decoration distinguishing one character from another.

The promised robotics show up in messages from the trees and a cell phone angle compromised by that tumultuous weather opening night.

This being Shakespeare, there's serious matter. "Cymbeline" is a play about stress between parents and children, both in families and among nations. But Quantum's lively yet elegant production is mainly a reminder that Shakespeare was above all an entertainer.

'Cymbeline'

Where: Quantum Theatre in Mellon Park (enter from Beechwood Blvd. or Shady Ave.).

When: Through Aug. 24; Wed.-Sun. 8 p.m.; also 8 p.m. Aug 19; no perf. Aug. 23.

Tickets: $25-$35; 412-394-3353 or www.proartstickets.org.