Other Desert Cities, Old Vic

Jon Robin Baitz learnt his craft writing on big American television shows including The West Wing and he created Brothers & Sisters, and Other Desert Cities - his first Broadway play - is another family drama with a political edge. The title comes from the signs saying “Palm Springs/Other Desert Cities” on motorways leading into the Coachella Valley, a vast sprawl of nine cities that have a profusion of resort hotels, spas and golf courses.

So here we are, in Palm Springs on Christmas Eve 2003, where novelist Brooke Wyeth (Martha Plimpton) has returned to celebrate the holiday with her well-heeled parents, younger brother and aunt after six years away. It's a showbiz family; dad Lyman is an actor-turned politician, mom Polly (Sinéad Cusack, pictured below) and her sister, Silda Grauman, once wrote cheesy comedies together, while brother Trip produces a Judge Judy-type TV show. Lyman and Polly's politics are Reaganesque (Nancy and Ron, their old friends, are referenced casually in conversation), while the three other characters are various shades of liberal.

At first it seems this is a happy family gathering as the play opens with the clan returning from playing tennis at the country club, but the clues to underlying turmoil are there. Silda (Clare Higgins) pokes fun at her sister denying her Jewish origins, Lyman (Peter Egan) won't talk about Brooke's older brother, Henry, who committed suicide some years before, and the family drink like fish despite Silda having just come back from rehab.

The long-awaited reunion begins to fall apart when Brooke tells them her latest book is not the novel they were expecting, but a revealing memoir that deals with Henry, who as a teenager became involved with a radical left-wing group and was implicated in a fatal bombing. Silda has secretly helped her write it, seemingly as an act of revenge against her more successful sister, who has turned into a brittle snob. Brooke, meanwhile, speaks loftily about a writer's responsibility and her pursuit of the truth - even if it comes at the possible cost of destroying her family.

Baitz's characters talk at length and with great articulacy about the egregious political right in America, the “indentured servitude” of being part of a family, the lies we tell ourselves, and how our memories can deceive us. It's a wordy play but Baitz has an ear for a clever line and there's much comedy in the first act, even if some of the gags are shoehorned in - “This water needs vodka for flavour,” says Polly, apropos of nothing.

Baitz gradually lets the skeletons out of the closet and our loyalties shift between the characters, but it's difficult to care about them terribly much. When the big reveal comes in the second act and we realise that nobody in this family is an entirely credible witness, it has less dramatic or emotional impact than it should – not helped by Egan's near inaudible delivery of much of the speech in which it comes. Lindsay Posner's direction is also sometimes underpowered on Robert Innes Hopkins's simple but evocative set, the first in a season of in-the-round productions at the Old Vic.

Daniel Lapaine plays Trip with real warmth and Higgins adds some spark to proceedings as the self-deluding and meddlesome Silda, while Plimpton - making her West End debut - imbues Brooke with a believable mixture of vulnerability and bull-headedness. The evening, however, belongs to Cusack, who is on cracking form as Polly; true, she has the best lines but she makes a monstrous character human, funny and affecting.

• Other Desert Cities is at the Old Vic until 24 May