Katie and the Snow Babies: Mermaid SOS: No. 8 by Gillian Shields
On the mermaid's route to finding the second Snow Diamond they discover that a baby polar bear and walrus have gone missing from their families and Katie and her friends vow to help find them. In gratitude, the chief walrus helps the mermaids to unravel the riddle which Mantora has devised to stall them in their quest for the next Snow Diamond.