The animals of Greenriver are in danger. Last spring, the otters' home flooded. Now the water is high again. Young otter Sedge believes he can save his holt from another flood - but he has to be brave enough to travel downstream for help. Downriver, the beaver lodge is also at risk. Silken - who is too small and weak to do the work needed to strengthen the beavers' dam - feels something calling her up the river. As the two animals unknowingly swim towards each other, they are drawn to the spirit of Greenriver, who takes the form of a snow-white otter, Lady River. But will Lady River hear their plea for safety?