TWENTY-FIVE years ago, Iolanthe the fairy married a mortal. The penalty for such an act being death, the Fairy Queen commuted the sentence to a life of penal servitude.

Strephon, Iolanthe's son from that union, is half-fairy-half-mortal - he's in love with Phyllis. Fairies, of course, never grow old, so when Phyllis catches Strephon caressing Iolanthe (who looks so young) she cannot believe it is his mother.

Love, treachery and death lie at the heart of the tale of Iolanthe, the first of two operas presented at the King's Theatre this week by the Gilbert and Sullivan Society of Edinburgh.

Iolanthe opened on November 25, 1882 at the Savoy Theatre in the Strand, London, a theatre that had been specially built to house the joint works of Gilbert and Sullivan, and ran for 398 performances.

"Since then, there's seldom been a time when it hasn't been in production somewhere in the world," says Ken Robertson, a spokesperson for Edinburgh's G&S Society. "After the big favourites like The Mikado and The Pirates of Penzance, Iolanthe is staged more than some."

If Iolanthe (Tuesday, Friday and Saturday matinee), however, doesn't quite quench your thirst for G&S, there's more.

The second piece, Orpheus In The Underworld (Wednesday, Thursday and Saturday) is based on Jacques Offenbach's original short two-act operetta with 14 principal performers and a full chorus.

It tells of Orpheus' descent into Hades to rescue his dead wife Eurydice from the clutches of Pluto, while the sub-plot sees the Gods on Mount Olympus begging to be released from their boring existence to experience the joys of a short break in Hell.

Truth be known, Orpheus In The Underworld wasn't an instant hit when it premiered at the Bouffes-Parisiens, Paris on October 21, 1858. It wasn't until a year later, when a critic with the Journal des Debats declared that it was "a profanation of holy and glorious antiquity" that the Parisian public began to flock to see it. In fact, after 228 performances the opera was taken off to allow the cast to have a rest.

They might not have quite as many performances as their predecessors but, having chosen to stage two shows in one week rather than their traditional one, the players of the G&S Soc of Edinburgh may soon know how they felt.

Robertson explains: "Each show has its own set of principals but shares the same chorus. We started rehearsing the two pieces in October of last year so this is actually the culmination of six months work."

• King's Theatre, Leven Street, Tuesday-Saturday, 7.30pm (Saturday Matinee 2.30pm), £10-£15, 0131-529 6000

LIAM RUDDEN