On a puddle jumpter test flight, McKay (David Hewlett) and a pilot suddenly lose control of the ship and crash into the ocean. Though he is able to communicate with Weir (Torri Higginson), he soon loses contact with Atlantis as he sinks lower and lower. Trapped in the back of the ship with almost no power and a badd concussion, McKay begins to hallucinate. Fortunately for him, his hallucinations come in the form of his intellectual rival, Samantha Carter (Amanda Tapping), who is ready to assist him in finding a way out. However, before they have time to formulate a plan,t he jumper descends to the ocean floor, and the impact causes a small break in the ship's hull, allowing water to sink in. Meanwhile, back on Atlantis, Weir and Sheppard have located McKay and devise a plan to rescue him -- but will they reach him before time runs out?