Interplanetary space explorers Rover and Speck have set out on a dangerous mission deep into the mysterious unknown: a visit to Unexplored Planet K2-18b. Though all seems calm to Rover when they first splash down on the watery surface, they soon find themselves in the mouth of a gigantic blubber beast! With a little ingenuity (by Rover) and some furious paddling (by Speck) they manage to escape unharmed. But when the pair meet two local spikey-spikes whose brother was swallowed by the Beast, Rover knows the brother's only hope is for the two brave explorers to go back inside the Beast to find him. Do Rover and Speck have what it takes to rescue the spikey-spike? Or will they--gulp--get swallowed, too?