The Party follows Martin Gilmour, a journalist shaped by his lifelong friendship with the wealthy and charismatic politician Ben Fitzmaurice. Having met at an elite boarding school, Martin and Ben have an unbreakable bond. Three decades on, Martin is invited to Ben’s lavish birthday party at the Fitzmaurice’s country pile, but Martin fears that the publicity of Ben’s bid for Conservative leader will dredge up the secrets of their past with tragic consequences.