Nobody does the dark and light nuances of human relationships quite as Ayckbourn manages it. Take A One Man Protest, the second of the quartet from the eight-play Intimate Exchanges sequence which has just joined the Mercury Theatre's repertoire. This highlights the disintegrating marriage of Miles and Rowena with Miles' colleague Toby, Toby's wife Celia, teenage home-help Sylvie and groundsman Lionel fluttering around its edges.

All six parts are played by two actors. Both Ruth Gibson and Gwynfor Jones have by now sifted themselves deep within their allotted trio of roles. Gibson reveals Rowena as a hippie free spirit whose teasing drifts into something more dangerous. Jones offers us a man who is on the surface a reasonable, caring human-being but who can (and does) tip over the edge when other people drive him to it.

Sylvie is another tease; Celia would – could – be one, but is too distracted by her own problems to offer more than superficial help. Toby is a man cocooned in his own self-sufficiency (for which read self-importance). Lionel is another man around whom any halfway intelligent woman is going to run the proverbial rings. Director Robin Herford has their measure, abetted by Michael Holt's set and some intriguing sound effects by Adam P McCready.

The protest of the title takes place in a garden shed, that repository for things (and people) no longer really needed to be in the house. We see an exploded view of it in the second scene, which is the heart of the play. What happens there leads on to churchyard encounters at that loneliest time of year for those not secure within a family circle – Christmas. What else will happen? You'll have to book your seats for A Pageant and A Game of Golf to find out. And even then, you may not feel that you've see it all...