Mariana Trench, the Pacific Ocean

With the help of his hero Ron Allum, Lars plans to dive to the bottom of the Mariana Trench in a submersible called the Deep Sea Challenger. Glitch plans to beat him there by sending a Grimbot in his Grimsub, but it can't withstand the heavy pressure of the water. Xuli and Lars must work together to mount a rescue operation at the bottom of the sea.