Rainsford was on the deck of his boat and he heard gunshots. This is inferring that there are people on the island. Moments later Rainsford loses his balance and falls of the boat. He is now stranded on this island.
After walking through the jungle for a while he finally finds a Chateau. It was set on a high bluff and on 3 sides of it cliffs divided down to where the sea licked greedy lips in the shadows.
General Zeroff is explaining to Rainsford that he hunts no usual animals. He hunts the most dangerous prey. The most dangerous prey is man.
Zaroff believes that Rainsford has given up and jumps off the cliff and into the sea. Rainsford then hikes out of the sea and to Zaroffs home and hides behind a curtain as he waits for the hunter.
Zaroff goes home to rest thinking that he won against Rainsford but he has no idea that Rainsford is still alive and is about to kill him while resting in his bed.
Rainsford kills Zaroff and then sleeps in his bed saying "I'm still a beast at bay."