Warriors of Ethandun — N.M. Browne

Dan and Ursula return to the present day after months in King Arthur's England. They sought a way back home for so long, but now find themselves unable to cope with modern life. Ursula's incredible strength and Dan's experience on the battlefield make it impossible to fit in with friends. So when they have an opportunity to go back in time, neither can resist. They emerge in 878 AD, the age of King Alfred the Great.

Vikings are rampaging through Britain and the King, defeated and weak, has retreated to the marshes. Dan finds him here, and he and Alfred's men begin plotting a counter-attack. But Dan cannot fight without Ursula. Consumed by her time-slip ability to wield magic, she has been captured by the Vikings who now revere her as a goddess. Everything hinges on Dan being able to rescue Ursula first from the Vikings, then from herself.

This is an utterly page-turning, clever, and action-packed finale to the Warriors trilogy.