"Now! Now you shall see what happens to those who would break the spell of mermaids!" Deep down in the underwater kingdom, Princess Finnglas is in the deadly grip of an evil sea monster, and the mermaids have bewitched Niall. Pangur Bán, the white cat, is desperate. He must rescue them—but how? Only Arthmael can do it. But who is Arthmael? And where is he? Can Pangur Bán find him in time?