How does someone go up, and not come down? Salim got on the London Eye, in a sealed capsule that took a half hour to view London. When the doors opened, he couldn't be found.
This was a very cool mystery. Part of what made it cool was the mystery itself, which has a fabulous twist near the end that confirms (or disproves) your theories and then throws them all out anyway. The other part of what makes it cool is the protagonist. Ted is a kid whose brain works with a different operating system, and it's just cool seeing the world through his eyes a little bit. Oh, also cool because it is an international book, being set in London and written across the pond and such.
The London Eye Mystery by Siobhan Dowd is a Cybils nominee, and I recommend it to mystery lovers of all ages and especially Lydia.