Whales on Stilts by M.T. Anderson

Imagine that you are Lily Gefelty. She thinks her father has a pretty boring job. But then she spends the day with him at the office. There are so many strange things going on. Her dad just tries to explain them away but Lily isn't buying it. Why is dad's boss wearing a disguise? And what is really going on? Lily and her friends decide they need to find out. She becomes convinced that stilt walking whales are about to take over the world!