Digit is going on his annual visit to Mermaidos, an underwater cybersite filled with merfolk, to visit one of his best friends in the whole cyber-world-Eugene. The two of them are great buddies who love to play underwater games, frolic with fish, and do other wacky water things in this idyllic underwater paradise. When Digit arrives, something is wrong. Mermaidos is murky and warm and the fish are leaving in droves. Digit feels terrible for his pal Eugene and promises to do what he can to make things right. It turns out Hacker has put a plan in motion to turn Mermaidos into his own personal hot tub! He is making the water hotter and hotter, raising the temperature to a hot 100 cyber-degrees- a temperature that would make Mermaidos uninhabitable for the Mermaidians and force them to move out. It is up to Digit and the CyberSquad to stop Hacker's plan, reverse the thermal pollution and help save Eugene's home.