Breathing apparatus is passed down to the two men through a small hole in the cavern roof, but each has only two hours of air in the tanks so there is little margin for error. The Sentinel arrives in New York harbour and Gordon sets off in Thunderbird 4 to find the inlet to the underground river. Scott tells Ned and Joe, now completely submerged to search for the river entrance from their end. TINY603.png|The water raises TINY604.png|Time running out Tiny613.png|Unloaded from The Sentinel Tiny615.png|Breathing gear on Tiny616.png|Waiting for air to run out Tiny621.png|Im on my way Tiny622.png|Dive into action Tiny623.png|The search begins