The London Eye Mystery by Siobhan Dowd

Main Characters: Brother and sister, Ted and Kat
Location: London, England
Time period: Contemporary
Genre: YA Fiction, Mystery

This is a really well-constructed locked-room mystery. Ted and Kat take their cousin Salim to ride on the London Eye--that huge ferris wheel-like attraction on the River Thames. Before they buy their own tickets, they are approached by a man who says he has a ticket he can't use. Since Ted and Kat have both ridden it before, they give the ticket to Salim and watch him get into the car. They keep their eye on the car the entire way around so they can greet him as soon as he gets off. But when the car arrives back at the starting point, Salim is not on it.

While their aunt panics and the police are stumped, Kat and Ted decide to try and solve the mystery themselves. Ted is the one who is able to come up the how because his brain is "wired differently"--he has Asperger's Syndrome and sees things in ways that others don't--while Kat is able to figure out the why.

Of course, now I want to take a trip to England and ride on the London Eye!