Drowned Ammet — Diana Wynne Jones

For centuries, Dalemark has been a land divided by the warring earldoms of the North and South. Now, with the help of the Undying, the mysterious gods of Dalemark, four extraordinary young people--from the past, present, and future--must join forces to reunify their beloved land.

TO AVENGE HIS FATHER, MITT JOINS IN A PLOT TO ASSASSINATE THE TYRANNICAL EARL HADD. BUT WHEN THE PLOT GOES WILDLY AWRY, HE FINDS HIMSELF FLEEING ON A STORM-TOSSED SEA, ALONE AMONG HIS ENEMIES--EXCEPT FOR THE FIGURE OF DROWNED AMMET....