Who is the antagonist in the London Eye Mystery?

In "The London Eye Mystery" by Siobhan Dowd, the antagonist is not a traditional character in the sense of a villain or adversary. The central mystery revolves around the disappearance of Salim, who goes missing during a ride on the London Eye. The antagonist in this case is the unknown force or circumstances that lead to Salim's disappearance, which the protagonist, Ted, must unravel through his observations and deductive reasoning.