During the time it took Keir Starmer to deliver his party conference speech this week, Caryl Churchill’s new play could be performed four-and-a-half times. This is partly because the Labour leader went long by rhetorical standards, but also because the 83-year-old dramatist’s later work tends (like that of Harold Pinter and Samuel Beckett) towards stinging miniatures. Over in 20 minutes, What If If Only might be subtitled Christmas Caryl, as, a man is, like Dickens’s Scrooge, visited by ghosts who confront him with alternative biographies. These apparitions, though, are not triggered by a miserly yuletide, but bereavement. The wedding ring-wearing protagonist sits at a table set for one telling stories across a single wine glass to the empty chair where a dead partner once sat. John Heffernan rawly embodies the lurches between memories of past closeness and the chasm of cold absence that grief’s derangement brings. The published text specifies spectres of Future, Futures, and Present, and in productions to come these might be differentiated, but director James Macdonald’s premiere gives all three to Linda Bassett. She skittishly sketches versions of our world that have, might, and would never happen, the last because they are too humane or sensible. In an upsetting conceit, one of the possibilities is a sort of unborn geriatric because history refused to deliver her. Using one actor for all possibilities emphasises the thin lines between different outcomes – a different word, gene, vote here or there, and everything changed. Churchill democratically leaves it to viewers to reflect on which presents and futures, personal and political, might be preferable or achievable. A note of optimism, or at least inevitability, is introduced by the brief but vivid entry of a Child Future, perkily played on first night by Jasmine Nyenya. Even such a sharp show will seem to many too short to justify a dedicated trip, but its 6pm and 10pm slots allow it to be seen as a double-bill with Aleshea Harris’s dark revenge drama, Is God Is, or, from next week, Lucy Kirkwood’s Maryland, a rapid response play to the murders of young women in London – forming an urgent Royal Court season on themes of death and fear.