Henry Perowne, a successful neurosurgeon, stands at his bedroom window before dawn and watches a plane – ablaze with fire like a meteor – arcing across the London sky. Over the course of the following day, unease gathers about Perowne, as he moves amongst hundreds of thousands of anti-war protestors in the post-9/11 streets.

A minor car accident brings him into confrontation with Baxter, a fidgety, aggressive man, who to Perowne’s professional eye appears to be profoundly unwell. But it is not until Baxter makes a sudden appearance at the Perowne family home that Henry’s earlier fears seem about to be realised...