The London Eye Mystery by Siobhan Dowd

The narrator of this mystery for middle schoolers is Ted who has Asperger's syndrome which is a high functioning form of autism. Ted does rather too much explaining how his brain works for the readers. That aside this is a pretty good mystery, not at all predictable in its ending.
Ted's Aunt Gloria and his cousin Salim are moving to the United States and want to visit one last time before they leave. Salim wants to go up in a huge ferris wheel called the London Eye as his last great thing to do before leaving. Ted and his sister Kat take him but a series of odd events occur, Salim goes up alone and seemingly never comes down. Police are called in, while they do their searching and interviewing, Kat and Ted do their own sleuthing. Ted with his very logical mind has made a list of possible explanation's for Salim's disappearance. Kat and Ted work their way through them, revising and eliminating and occasionally lying and sneaking which Ted finds especially difficult. While the kids and the police often find they are going over the same territory, it is Ted who makes the final correct deduction. And really it was only logical. Short and fun. JDW 4/22/08