One morning, Molly's dog Gus goes missing and the whole island are sent searching. On her search, Molly and her friend Bo hear a noise coming from a cave and decide to follow it. As they head deeper into the cave, Molly and Bo finally find Gus but the tide begins to rise. Will Molly, Bo and Gus be able to make their way out of the cave before... -- Cyngor Llyfrau Cymru