The Infinite Sea by Rick Yancey summary (2nd book of the Fifth Wave series)

     This book picks up a week or so after the group initially escaped Vosch's camp, with them hiding out in an abandoned hotel while Cassie waits for Evan, although he is believed by the other group members to be dead.
     They all know they can't stay there as Vosch and his army of brainwashed kids will be looking for them, along with the fact that winter is coming and they will freeze and starve to death where they are now.
     Ringer says there is a network of caves not far from their location that they could stay in for the winter and she leaves to go scout it out to see if any other survivors are there.  Teacup takes off after her and when she sneaks up on Ringer, Ringer thinks it's a Silencer and shoots her.  She hears a helicopter coming and runs out to meet it knowing it's the enemy and they will take them back to camp just so that they will save Teacup.
     The book switches to Evan's POV, and after collapsing while trying to get to Cassie after the explosion he wakes up in a cabin with a woman named Grace, who turns out to be someone Evan had met when he was younger after he was first "awoken" in his body and he found out she was an Other too.
     Grace asks who Cassie is as he was mumbling her name but he doesn't want to talk about her since he knows Grace despises humans.  He stays with her for a while to try to act like he's on her side while recuperating from his injuries and come up with a plan to get away from her.  He knows that if he doesn't kill her she will follow him right to Cassie and the others.
    There is a space mobile hanging above the bed in the room he's in, and when Grace attempts to seduce him he takes the wood from the mobile and hits her with it over and over again.  Thinking he has killed her he takes off but she awakens and follows him.
     He makes it to the hotel but knows that if he just walks in they'll kill him as he's too weak from his fight with Grace to be able to confirm his identity before they shoot thinking he's an Other (well, he is, but you know what I mean, a bad Other).
    After he knocks Ben out, he sees Cassie's little brother and starts to head toward him so he doesn't shoot him but Cassie comes up behind him and knocks him out not knowing who he is.  After realizing it's Evan she bandages his wounds and tries to nurse him back to health like he did for her.
     A little girl shows up who turns out to be a friend that Cassie's brother made while they were at camp and Evan tells them they can't get near her as an IED is implanted in her throat that is programmed to be detonated when enough CO2 is present, and that this is what Vosch had been using all the little kids for that were too young to be made into military.  He would drop the kids off at known survivor locations, and when the adults would find them the CO2 of their breath would detonate the IED.
     Cassie performs surgery on the little girl and manages to get the pill like IED out of her and they place it in a baggie.  They plan on getting CO2 canisters from the convenience store near them and placing the canisters and the IED in the elevator shaft so that the slow leak will cause the bomb to go off after they are a safe distance away, making Vosch think his plan worked.
     Grace shows up before they have the chance to do so however, and when she attacks Cassie they all fight back and she barricades herself into one of the rooms in the house.  Evan convinces Cassie to leave with her group as he knows it's only him that Grace is interested in for the moment and that she must have orders to bring him back to Vosch since she's taken so much effort to follow him.
     When they leave, Poundcake is being carried by Ben, as during the fight with Grace he was shot.  They realize Poundcake isn't going to make it and leave him behind but he makes it back to the house and finds the baggie with the IED and sacrifices himself by breathing on it to make it go off and kill Grace while she's in the house with him and about to finish him off although she sees he's already dying.
     It switches to Ringers POV, and Vosch is keeping her hostage at one of his camps (not the same original camp of course since it's been blown to smithereens).  He tells her he's going to run an experiment on her and he injects her with an enhancement serum.

*****ok, so I'm confused on this part and I'm not sure I'm interpreting it right, but hopefully I am.  If you think differently please let me know******

     He reveals to Ringer that there were never any aliens, that the people like Evan and Grace were really just enhanced (like she is about to be) by other humans like himself and were brainwashed into believing they were Others.
      It's never explained though why humans would even do this to wipe out all the rest of humanity or what, so I'm not sure if there ARE aliens behind all this or if it really just is some human scientists who took it upon themselves to clear out the world. Big old question mark on this part of the book for me.
     Ringer escapes with the help of Razor, her caretaker while she's been recuperating from the enhancements.  She has fallen for him and they develop a kind of code through chess where he tells her he's going to help her escape.
     Turns out that was just a lie too, because after the escape he leads her right to Vosch in a barn where he says he's hiding Teacup.  She tries to kill Vosch but fails and Razor stays there with her.  This is another part I'm confused on....why does she stay with him if he turned her in to Vosch?  How could he have been forced to do it if they had already escaped? Did Vosch recapture him while he and Teacup were trying to meet up with Ringer after the escape?
     Anyway, after they do some hanky panky he tries to convince her to run but she won't do it knowing that Vosch has Teacup so she goes back to the base to get her.  Vosch meets her there with Teacup and tells her she will be his weapon now or Teacup will die.  Razor then shoots Teacup and tells Ringer that she has no excuse now and she needs to run.  Vosch shoots and kills Razor and Ringer takes off.
     The book ends by going back to Cassie's POV.  She has told Ben that they are going to the cabin that Grace was staying in under Evan's directive, as he said that there's a pod that will drop there with supplies for when Grace was staying and if she can find a way to put a bomb in the pod when it's sent back up to the mothership (another thing I'm confused on, if there's no aliens where the heck did the mothership come from?) that she'll be able to end everything.
     Cassie once again thinks Evan is dead but she sees him come limping towards them from the direction of the house and she goes to meet him.

End of book 2