dr. richard harris. the shot not just to relax each boy, it was to knock him out cold. >> i was not fully confident we could get them out alive. we weren't sure how they'd react in the water, whether the drug would be enough. >> reporter: once sedate a face mask strapped tightly on each one, a potential leak fatal. >> when they start moving, arms moving around, the potential for them to kill themselves, the potential for them to kill us. >> reporter: but he's not one for turning back. he entered the cold, murky water with the boy fort daunting first dive stage. remember, 350 meters long, 3 1/2 football fields. after about 20 painstaking, agonizing minutes, mallenson successfully completed the first stage. waiting for him were two support divers who helped him lift the unconscious boy out of the water. >> we realized that the mask worked, the drug worked. after that i new there's a good chance we can get them all out. >> reporter: the three had to physically carry the child to the next dive point, then sw