Triangle's Overlapping Timelines Finally Explained

When Jess One boards the ship, Jess Three has become the masked killer, and Jess Four is keeping a low profile. After the group is separated, Jess One is attacked by Victor and accidentally kills him in the banquet hall, discovering that his head had been previously impaled. Masked killer Jess Three then shoots and kills Downey, Sally, and Greg from Group One. After their deaths, Jess One fights Jess Three, and Three is forced overboard into the water.

Once Jess Three is off the ship, Group Two arrives, and when Jess Two boards, Jess One and Four are already present. Jess One then accidentally impales Victor from Group Two. However, in an attempt to break the cycle, she confronts Jess Two in the banquet hall. Jess Two runs off, with both leaving an injured Victor behind them. 

Meanwhile, Jess Four puts on the masked outfit and kills Greg from Group Two, but Jess One is able to protect Sally Two and Downey Two, and she injures Jess Four. Jess One then leaves to search for Victor Two, who she finds has been thrown overboard. Meanwhile, Jess Four finds and stabs Downey and Sally to death. After Sally dies, Jess One witnesses Jess Two bludgeon Jess Four to death. Afterward, Group Three arrives. 

Now, realizing that the sailboat returns when everyone is dead, Jess One puts on the masked disguise and the prior events of Group One repeat themselves, with Jess One now doing what Jess Three did earlier. Jess One shoots and kills Greg, Sally, and Downey, and just like before, gets into a fight with Jess Three. This time, Jess One is thrown overboard, and washes ashore before running home to her son.