Greenlake Gateways 1: Tins, Trolls and Valiant Vikings

Riya can't catch a break. She's being teased by her class rival, needs help with her school work and, to top it all off, she's fallen through a gateway in time to battle giant trolls alongside some Vikings!
Can Riya defeat the trolls, help the Vikings and escape back through the Greenlake Gateway? All in a school day's work...