Marietta Kirkbride's one-act two-hander, Sitting With Thistle, is set in a remote country cottage. Outside it's been snowing heavily for a week. The atmospheric sound of the whistling wind greets us in the dimly lit space, which is cluttered with all sorts of artefacts: pots and pans, jars, sheep skulls, quails eggs etc. These belong to Alice, who lies dead, wrapped in a blanket. She is, or was, the grandmother of Mark and Elysé, a brother and sister in their twenties, who find themselves trapped together, with just each other for company, deciding what to do until help arrives.

Mark (Mathew Foster) is teasing, puerile and restless and Elysé (Pascale Morrison-Derbyshire) is more considered and mature, but equally nervy. But while there is convincing banter between the siblings, there is a slow-paced build up of tension which seems too contrived, as their history and mutual disdain for each other is revealed over the drawn-out ninety minutes. We learn Elysé is a haemophiliac and therefore must be careful not to sustain an injury… cue an injury later on, caused by Mark. Meanwhile, Elysé blames him for the break-up with her boyfriend after Mark secured a job for him abroad where he met another girl.

They play futile games with each other (hangman on the wall of the cottage) but cannot settle any old scores until we discover what caused the childhood rift in the first place. The Thistle referred to in the title was the family dog. I won't reveal how this has impacted on the siblings' brittle relationship, save to say that it wasn't exactly something which should have carried through to adulthood. That is, not without offering some meaningful dissection of the supposedly severe traumatic circumstances which appeared to trigger Elysé's condition.

Admittedly both actors are convincing as the digging duo but the script and pace need tightening to give it a little more credibility and the dramatic intensity it deserves – I wonder if having two directors, Simon Kane and Elf Lyons, rather than one affected this. The device used to make them confront each other (being trapped with a dead body) does reference the original trauma. However, new wounds replace the old wounds that have been reopened, as the play comes to a sudden but unsatisfying conclusion.

Sitting with Thistle, at Lion and Unicorn Theatre

Some good moments cry out in this tense and pensive piece about a brother and sister on the edge of resolution after years of ignorant hostility. But the strain of having a dead body in the room isn't quite sustained. At the Lion and Unicorn Theatre.