Mirlings live in the garden fishpond. When Molly meets newcomer Flash, their dislike is mutual. But it becomes difficult to avoid each other after they and Molly's friends are netted with goldfish destined for an indoor tank. Can the mirlings stay hidden from the humans while surrounded by glass? Will river-born Grandad end his days in a fish-tank? Will Flash's recklessness endanger them all? Will the humans ever master fishkeeping?