It's presumably the end of the mission, because Scorpion has gone far enough south that it can surface without fear of radiation. The crew is beyond psyched to finally see the sun.
To make a long story short, they found nothing. Zilch. Nada. You get it, right? They spotted a dog on shore, but there was absolutely no sign of human life.
Peter, Dwight, and John discuss the war as they cruise home. John reveals a few key details: there were "four thousand seven hundred" nuclear weapons dropped, which is insane (3.34).
The guys also discuss a bunch of hypothetical reasons why the war broke out (it's nuts that no one knows), but they have no way of knowing for sure at this point.
Here's something crazy that they do know, however: America bombed Russia under false pretenses. Although Washington had been hit by a Russian bomb, it was in fact sent by Egypt in response to American involvement in the Israeli-Arab war.
At a certain point, every major capital city had been destroyed, which meant that all the politicians were gone, too. That left a bunch of inexperienced military men in charge, which escalated the conflict even further.
At noon, Scorpion docks with the naval base. Dwight meets with the admiral and reports on their (lack of) findings: the only interesting note is that the crew came down with "measles" (3.105).
Peter calls Mary and tells her that he'll be home tonight. She's a little worried about Jennifer catching the measles, but she's super excited to see her bae.
Mary calls Moira when she hangs up with Peter. Naturally, the conversation turns to Dwight, with Moira arguing that she has no chance with a "married man" like him (3.161).
When Peter returns home, Mary makes him promise to invite Dwight over. He shrugs, but agrees; he has to head back to Williamstown to meet John tomorrow, anyway.
After their meeting, John and Peter go to a fancy place called the "Pastoral Club" for lunch (3.176). There they meet John's uncle, Douglas Froude, and he is getting hammered.
Meanwhile, Moira has just called Dwight. She demands that he accept Peter's invitation to visit (only if he asks, of course). After she hangs up, she calls Peter and demands that he invite Dwight over. Pretty sneaky.
Next thing we know Dwight and Moira are meeting at the train station in Falmouth, where she and the Holmes family lives. As usual, they stop off for drinks on the way home.
Dwight tells Moira that he thinks Scorpion will be sent on a mission to the U.S. He doesn't give any more details, but that's a very interesting prospect.
After stopping by the Holmes home for a lovely picnic, Dwight and Moira decide to go sailing. This time the boat remains righted, and all bras remain firmly attached to their bodies.
As Dwight and Moira lounge on the beach afterwards, they discuss his journey to America. There are some real dangers: namely, the "minefields" that block "every major port or river entrance" (3.276).
Dwight briefly tells Moira about his home in Connecticut, which is saturated with so much radiation at this point that he couldn't visit even if he wanted to.
Dwight talks about his family, too. What's odd is that he speaks about them in the present tense, as if they were still alive, waiting for him. Must be hard to face the reality of the situation…