The silver arrow

the long version

"Finna has lost her father in a horrible shipwreck, and now her Great-grandfather is missing. Using clues from hidden papers written with a secret code, Finna, her twin brother Erik, and their best friend Kalli set out to solve the mystery. They follow the trail from the Snæfell Mountain to a cavern under the Icelandic glacier and through a mysterious vortex. Along the way, they encounter strange and terrifying creatures, Nordic gods, and an alien civilization. After her brother and best friend are kidnapped, Finna finds she must use her archery expertise, an ancient artifact and all her courage to save them and an entire planet. The fate of the alien world and the future of Earth depend on her true aim!" -- Back cover.