IF you plan a

bucket-and-spade holiday in West Wales with your in-laws, give this play a miss. Otherwise catch it if you can at Dundee Rep or next month at the Tron Theatre in Glasgow (it's a co-production).

Sharman MacDonald's bittersweet new piece is a gem, cleverly constructed, wittily written, shot through with keen observation.

Two sibling families meet on the beach for their hols in 1961 - a frought encounter where tensions and passions surface, where childhood aches jar with the frustrations of adulthood. One father is a bit of a lad, the other, his brother, buttoned-up: one wife plump and cuddly, the other

(Alison Peebles) embittered and disappointed.

Sea, sand, and the sound of music - guitars are in, which means that several actors have to strum, which they do competently. Mood music at times - there are moments when Checkhov is a presence on the prom. The children (there are three, with alternating casts) perform bravely, and I particularly admired Natasha Gray, who played the exacting role of Rena on the opening night.

Her heartfelt invocations to ''Mr Manning'', the Glasgow serial murderer, inviting him to join them at the seaside and make his ninth killing - herself as victim, when she's feeling really low, but mostly she volunteers her cousin - is a nice conceit of the author. Sea Urchins started life as a radio play and in this version written for the stage some traces of its origin remain. It's no bad thing - indeed the challenge prompts many ingenious touches by the director, Irina Brown. Jacqueline Gunn's abstract set is strikingly effective.