Complex sentence: After Nate co-operates with Eddy to fight for their lives, he and Elena escape when Eddy is killed by the creatures, and find themselves in an abandoned Nazi submarine base built into the island.
Split into simpler sentences: After Nate co-operates with Eddy to fight for their lives, he and Elena escape while Eddy is killed by the creatures. They find themselves in an abandoned Nazi submarine base built into the island.