Mary Pope Osborne is the author of over forty books for young people. She was the president of the Author's Guild, the leading organization for professional writers in the US, for two years and has won many awards for her books. She lives in New York with her husband, Will, and their dog, Bailey, who sleeps on top of Mary's desk every day while she writes.

A tale of high waves and high adventure for Jack and Annie when the tree house lands in the sea off the coast of Ireland. Things get dangerous when Viking ships approach!