The rising action begins with Rainsford's realization that Zaroff will hunt him. It continues all through the hunt and ends when Zaroff believes Rainsford has fallen to his death off the cliff. Rainford's supposed death is definitely the turning point in the story; some would argue it's also the climax. Others will say Rainford's surprising Zaroff back at his chateau is the climax, but I tend to think it is the resolution.
In any case, the falling action is rather implicit and time-compressed. We must deduce that it includes Rainsford swimming back to the chateau in order to hide behind the curtain. Zaroff must hike back there too. The falling action also includes the dialogue between the two before they fight. That would make the fight, then, the resolution (although we flash forward through it). And the last sentence, about Rainsford never sleeping better, is the denoument.
Good luck on your plot diagram...