Martin savors the fine spring weather as he wanders the woodlands with Gonff and his new friend, Skipper, the otter. Their carefree excursion is interrupted by a party of soldiers led by Tsarmina. She demands the return of her two prisoners, but Skipper says she doesn’t rule Mossflower Woods. A fight breaks out, with squirrel archers aiding in the defense. When Tsarmina gains the upper hand, a group of otters dives into the river, carrying Gonff and Martin with them. Angry at losing her quarry, Tsarmina orders Fortunata to fetch the fearsome monster known as the Gloomer because nothing can escape him underwater.

The otters bring the two mice to their underground caves: “It was a large, sandy, shelflike area, the roof of which was a mass of gnarled willow roots. Phosphorescence from the swift-flowing water palely illuminated the cave system of the underground bank” (75). Skipper says everyone will be safe here. One of the otters who stayed behind to spy reports that Tsarmina will be sending the Gloomer.

Back at Kotir, Fortunata and a group of soldiers journey to a watery lake in the depths of the fortress, where the giant water rat named the Gloomer is chained.