The 5th Wave by Rick Yancey

Spoilers!!! 
This post contains lots of spoilers!!

Cassie (short for Cassiopeia because of course) is trying to survive an alien apocalypse. The book begins in the 4th wave, but there are flashback to the previous waves. The 1st wave was a huge EMP that turned off all electronics. The 2nd was massive flooding that destroyed most coastal cities. The 3rd was a plague that killed millions (including Cassie's mom). The 4th wave are Silencers - alien assassins that look like humans, which makes us unable to trust anyone else. Silencers killed her dad and took away her little brother, Sammy. She gets shot by a Silencer, but eventually is saved by a cute teenage boy named Evan. She stays with Evan until she recovers. He falls for her. She likes him, but still feels like something is a little off about him. She's determined to rescue Sammy, who she believes was taken to Wright-Patterson army base. Evan doesn't want her to go by herself and she agrees to let him join her. 

Meanwhile, at Wright-Patterson, Ben Parrish (who, btw, Cassie had a huge crush on in high school) is sick with the plague and staying in the camps outside the base. The camps are attacked, but he's brought inside where he recovers from the plague. They convince him that some humans are actually aliens and that they can train him to fight them. He goes through training with other kids - some as young as 7! He's now known as Zombie. Eventually Sammy (aka Nugget) joins the squad too, but of course Ben doesn't know him. But they quickly become close. Their squad finishes first out of all the other squads and they go on a mission (except Nugget, he's deemed too young and has to stay behind to train more). On the mission, they figure out that they're not shooting at aliens - they're shooting at other humans! They have an eyepiece that helps them tell who's who but they realize it just shows them who has the tracker they were given or not. Ringer (the girl that Ben likes) convinces everyone to take out their trackers. Ben decides that he needs to go back for Sammy.

Cassie finally figures out what's weird about Evan - he's an alien! Apparently, some humans were implanted with alien consciousnesses when they were younger and they awoke a few years ago. Evan's job is to "cleanse" the earth of humans. But he fell in love with Cassie instead. She's freaked, but quickly becomes okay with it. She still decides to try to save Sammy, while he stays behind, just outside of Wright-Patterson. Action ensues, and Cassie and Ben basically get to Sammy at the same time. Evan finds them and saves them after they're captured by the aliens. Cassie and Ben escape with Sammy, but Evan stays behind to destroy the base. Just in time, Ringer comes back and saves Ben, Cassie, and Sammy. 

The Living by Matt de la Pena

Spoilers!!! 
This post contains lots of spoilers!!

Shy is from a poor neighborhood in Southern California who gets a job on-board a luxury cruise ship. His grandmother just died from a mysterious new disease. He's made new friends on the cruise ship, including Carmen, who he's secretly in love with even though she's engaged to a guy back home.

On his first cruise, a guy commits suicide right in front of him after talking about what an awful person he is. On his second cruise, there's a creepy guy in a suit that is watching him and eventually confronts him, wanting to know what suicide guy told him before he died.

A huge storm hits the ship. During the storm they get word that California has been hit by a massive earthquake. Really massive - off the Richter scale. And that means tsunamis. The ship is hit by several tsunamis. Shy is separated from his friends but survives, even though many people die. He eventually makes it to a raft with a few other crew. Their raft is hit by another tsunami and Shy abandons the raft. He happens upon a lifeboat that has been badly damaged. Everyone inside is dead. He's able to patch the hole in the bottom but it won't start. He comes upon a sinking raft with a few people left. And there are sharks circling. Several don't make it, but two are able to make it to the lifeboat. However, one of them is bitten and eventually dies. Before dying, he slips Shy a huge diamond ring that he was planning on proposing to has girlfriend with. The other person that makes it to the lifeboat is a spoiled teenage girl named Addie. They fight at first but eventually learn more about each other and come to like each other (and Addie seems to kinda fall for Shy, but he's still pretty hung up on Carmen, hoping she's still alive).

They have one oar and use it to go in the direction of some islands that other passengers have talked about. Addie's dad works for some secretive medical company on the islands. They come across an abandoned motorboat with two dead scientists on-board and a duffel bag with unmarked medications. The controls are destroyed so they stay with the lifeboat, but Shy takes the duffel bag with them.

They are eventually rescued by another motorboat with Shoeshine, an older crew member from the cruise.

Independent Study by Joelle Charbonneau

Spoilers!!! 
This post contains lots of spoilers!!

This book picks up about six months after the Testing. Cia has been taking general studies courses. Everyone takes a test that will decide which area they will focus the rest of their studies on. Cia wants Mechanical Engineering but ends up with Government. 

She begins to remember bits of her time in the Testing, which makes her more curious. She wonders what happens when students are "Redirected" and after snooping around, figures out that they are likely killed. Michal tells her of the rebellion that he's a part of that wants to remove Dr. Barnes (head of the University and Testing). The rebellion has 2 factions: Symon's (to which Michal belongs) that wants to achieve this peacefully, and the other that is tired of waiting and wants to use violence. Cia agrees to help in any way she can.

The new government students go through an Induction, which is basically a mini version of the Testing. It's basically a group scavenger hunt that tests many skills. Cia's group comes in first. Her upperclassmen mentor Ian warns her that Dr. Barnes and Prof. Holt are watching her because they think she did too well. They've set her up for failure by assigning her more classes than anyone else. Cia manages to make new friends among the government students - notably Enzo and Raffe.

Cia is still together with Tomas, but she's warned from seeing him by Ian. She begins to suspect that Tomas still has his memories from the Testing. She confronts him and he confirms that he does. She asks what happened to Zandri and he admits that he did kill her, but accidentally. She's upset, but is able to forgive him.

Cia is assigned to an internship with the president. She discovers that Michal is also working there. He tells her that the president is about to introduce a bill that would restrict the power of the Testing officials. But he's afraid she'll lose the vote, which will make her look weak, which will likely prompt a vote of confidence that she would likely lose. Then Dr. Barnes could ensure that someone friendly was appointed to the position. They need proof of how evil the Testing process is. With the help of Tomas and Raffe, Cia is able to get the recordings their bracelets made during their Testing. She hands then over to Michal, who takes them to Symon and the rebellion. Cia and Raffe tag along but remain hidden. When Michal hands over the recordings, Symon shoots and kills him. Cia is horrified, but then recognizes his voice and someone she overheard conspiring with Prof. Holt - Symon has been working with Dr. Barnes to sow a fake rebellion so that those who would want to rebel would have an outlet, but no actual chance at actually succeeding.

Cia also recognizes her brother Zeen among the rebels. Apparently he has left home to look out for her. She is able to use the transit communicator to make contact with him at the very end of the book.