"While journeying to the northernmost reaches of the Arctic, April Wood discovers a tiny polar bear cub in desperate need of her help, and in freezing temperatures and on dangerous terrain, she must face her deepest fears to save him"--

Their magic tree house takes Jack and Annie to the Arctic, where a polar bear leads them onto very thin ice.

"There are no polar bears left on Bear Island. At least, that's what April's father tells her when his scientific research takes them to a faraway Arctic outpost for six months. But one night, April catches a glimpse of something distinctly bear shaped loping across the horizon. A polar bear who shouldn't be there--who is hungry, lonely, and a long way from home. As their unlikely bond grows, April is determined to save her new friend--and so begins...