Complex sentence: Sawyer and Kate carry out an elaborate escape plan, but he is caught by Ben, who knocks him unconscious and operates on him, implanting a pacemaker that will malfunction if Sawyer's heart rate exceeds a certain point.
Split into simpler sentences: Sawyer and Kate carry out an elaborate escape plan, but they are prevented from acting on it when Sawyer is knocked unconscious by Ben. The Others operate on Sawyer, implanting a pacemaker that will malfunction if his heart rate exceeds a certain point.