We jump back to 20 minutes before the chemical attack. James got a good night's sleep after having spent the evening with Tani. Later, his SEAL pal, Hopper, lunges at Marcus after an uneasy conversation about their mission in Pakistan. The captain wants a video chat with Secretary of Defense Curry, but Nigel is in a particularly feisty mood. He plops a picture of Christine Kendal being held close by Paul Wells on the video screen. Sam is flustered. As for Nigel, he loses it completely loses it when he trashes a bank of electronic equipment. So much for the video feed.
Tani nearly steps off a cliff when she thinks she sees her dead mother. James looks out to see a Black Ops team streaking towards the island in a Zodiac boat. Not good. Back inside the Early Warning Station, Prosser realizes that the reason everyone is acting loopy is because they've been dosed with a nasty drug nicknamed "The Buzz" by the military. It causes delusions, poor judgment, paranoia, hallucinations and, ultimately, unconsciousness. On the bright side, it lasts only eight hours and it doesn't kill you.
The search is on for Epinephrine shots to snap folks out of their haze. Marcus, Grace and Prosser take the Colorado out with a skeleton crew to keep it safe. Unfortunately, someone has swiped all the Epi shots onboard. The crew is dropping like flies. The bad news continues when a fire breaks out in the Oxygen Generator Room. A woozy Grace takes the Conn while an equally-unsteady Marcus heads below. Along the way, he sees visions of his son, Jeffrey, running through the sub. Meanwhile, the oxygen tanks are down. Soon all air in the sub will be gone
We jump ahead to three hours after the chemical attack. Sam teams with James to hunt down Serrat, who is hanging with the Black Ops. They are trying to revive Sophie to reestablish communications. The Ops team has Hopper tied up. Their leader is a trained killer named Booth. Sam has seen this guy before. About an hour after the attack, he passed himself off as a member of the Colorado crew. He was fixing up the broken arm Hopper gave him when the snatched him. Sam figures out that the guy is a fraud. The brawl that ensued after this realization explains the bloody wounds later seen on each man's face.
In present time, Booth orders Sophie downstairs to reset the power for the antenna. He lets Serrat know that she's dead as soon as the job is done. Sam and James quickly take out the Black Ops team. They do so with the help of Serrat, who shoots Booth before the guy can kill Sam. A deal was made to drug everyone so that the Ops team could recover James and Hopper. Serrat played ball with them so he could get his island back.
On the Colorado, a fading Prosser tells the captain that he needs to turn the oxygen back on. Unfortunately, Marcus can only sit in a corner. He's telling a story to the hallucination image of his young son. Then he passes out. A short time later, Marcus awakens with an Epi syringe sticking out of his chest. Someone has turned the air back on. But who? Marcus heads back to the Conn as the oxygen levels rise. He lets Sam know that they'll return to the island once the rest of the crew awakens.
Hopper lets James know that he received a change in orders regarding their mission in Pakistan. They were to eliminate the man they were initially sent in to save. Elsewhere, Marcus lets Sam know that someone on their crew may have helped set up the chemical attack. It may be the same person who stole the captain's firing key while he was unconscious. Without that key, the Colorado has no nuclear launch capabilities. They are completely defenseless. Marcus and Sam need to find that key ASAP.
Sam saw visions of Christine in the hours after the attack. He doesn't remember much of what went down while he was in his woozy state. He shared a passionate kiss with his vision of Christine, who wanted to know what he was doing. It seems like an odd thing for a wife to ask her husband, even in a dream. That's because the person who asked Sam the question in reality was Sophie. She watches the scene play out in a video that was recorded by a security camera. Sophie is clearly unnerved by this, perhaps because she didn't resist Sam's kiss.