Max Darwin is called back to Bug Island to bolster the bugs' defenses. Emperor scorpion Spike has found a tunnel that leads directly from Bug Island to Reptile Island-a dangerous hole in their defences that they have to plug, fast! In the dingy tunnels beneath the island, they encounter some prehistoric mega-bugs, only too happy to help their bug cousins against the reptile threat. The huge centipedes and long-lost giant snails are impressive creatures, just what the ranks of the Battle Bugs forces need. But lurking in the shadows is a prehistoric snake in the shape of Lieutenant Titan standing in their way. Unless he's defeated and defences are restored, Bug Island will be a sitting duck!