Dan and the Shard of Ice by Thomas Taylor
Dan can see ghosts. See then, speak to them, and sometimes help them...for a price. In his third adventure, poltergeist activity is plaguing one of London's tallest, oddest buildings, the Shard. Dan must try to fight off an enraged spirit and a very much alive fraudulent medium, while saving a little girl, working out what his ghostly sidekick is hiding from him and not plummeting to his death. Some of those things will be easier than others. An exciting, funny urban fantasy with a dark gothic twist.