Why is the deck hand behaving so suspiciously? And what is in the letter he keeps studying?
On the Whanganui River Mary Paul's grandfather runs a small fleet of boats servicing the settlements along its banks, and his arch-rival, Alexander Hatrick, owns a larger fleet that goes further up the river. When Hatrick's nephew Tom arrives from England, he immediately puts Mary's back up with his arrogant manner, adding to the ill-feeling between the two families.
But Tom persuades Mary to take a tirp with him on his uncle's boat to the grand Pipiriki House Hotel, and convinces her and her brother and sister there's something suspicious about one of the deck hands. Then suddenly Mary finds herself in a very dangerous situation.
The children become caught up in a mystery that involves hidden jewellery, a well, a Rookery - and a thrilling chase up the rapids of the Whanganui River.