Book 4 time! I'm really excited about this one because it has a couple of my favorite bits out of everything I've memorized.
Story so far: Satan has picked himself and his fellow demons up from the lake of fire in Hell, and they decided to send him to scout out this new world where God has said he's going to create some new creature called "Man". He's made his way out the gates of Hell, found his way through Chaos and Limbo to the Sun, where he's fooled Uriel into giving him directions to the garden where Adam and Eve live.
Now in book 4: After a very brief introduction from Milton, bemoaning that there's nothing he can do to actually warn Adam & Eve, we pick up with Satan approaching the Garden. Before he gets there, though, he takes a few minutes to vent about how depressed, sorry, and trapped he feels. He considers repentance, but knows that he'll never be able to make it stick...so on he goes in the cause of evil. He reaches the garden, finds that it's at the top of a large steep forested hill over a river, and leaps over the circling walls of trees into the Garden of Eden proper. The garden is described in loving detail, and we (and Satan) finally get our first proper look at Adam and Eve, whereupon he promptly falls in love with them and gives another anguished monologue about how sorry he is to be hurting these innocents (but he's going to do it anyway). He spies on Adam and Eve while they talk with each other (Eve, notably, tells of her first experiences with existing, which is my favorite bit!) and learns that there's a tree they've been forbidden to eat from - he leaves to explore the rest of the Garden as Adam and Eve go off to bed (and to make sweet, sweet love, which Milton defends at length).
Then we cut to Gabriel, whose job is to guard this paradise, as Uriel comes from the Sun and warns him of Satan, who Uriel has now realized is not as innocent as he appeared. Gabriel sends out some scouts who successfully find Satan trying to mess with Eve's dreams as she sleeps - they arrest him and bring him to Gabriel. Satan and Gabriel yell at each other for a bit, then prepare to fight, but God sends an astrological sign that Satan takes as a warning that he'll lose if he does, and he instead slinks off as night ends.