River Secrets — Shannon Hale

Razo has never been anything but ordinary. He's not very fast, or tall, or strong, so when he's invited to join an elite mission escorting the ambassador into Tira, Bayern's great enemy, he's sure it's only out of pity. But when they arrive in the strange southern country, it is Razo who finds the first dead body. As they try to learn more from the Tirans about the ever increasing murders, Razo is the only Bayern soldier able to befriend both the high and low born, including the beautiful Lady Dasha. And as Razo finds allies among the Tirans, he realizes that it may be up to him to get the Bayern army safely home again.