Ryan Keene works for the Navy's Marine Mammal Program. He and his sea lion companion, Hansel, search and retrieve equipment lost in the oceans depths. Their latest mission is in the vast Artic region. Usually these missions are straight forward, but an armed Russian oil company is paying close attention to the recovery. The next thing Ryan knows, he's on the run with Hansel across the Artic ice toward a Finnish Research station. While hunted by the Russians, he must worry about staying warm, eating enough food, and avoiding polar bears and walrus herds.
This is an excellent book for 4th and 5th grade boys. It's packed with action and weaves in factual information about oil drilling, environmental changes, animal training, human and animal survival in extreme conditions, and the global fight for Arctic territory. Highly recommend this and London's other series Dog Tags.