Cassie- main character, told in first person narrative from her pov
Ben Parish/Zombie- love interest, another main character's pov
Vosch- an Other posing as human military
Cassie's Dad- I don't think his real name is ever mentioned; same for her mom
Sammy/Nugget- Cassie's younger brother
The Others- aliens who have attacked Earth
Evan- the Silencer aka love interest
Ringer- female soldier in Bens squad
Dumbo,Flint,Pound cake, Teacup- Ben's other squad members
The book begins with Cassie trying to survive day to day and hiding from the drones of the Others which patrol the skies looking for humans still alive. She goes one day to search for water at an abandoned gas station and hears someone inside. It's a man who has been shot, but it's 3 weeks into the 4th wave and she knows humans can't be trusted. When she tells him to show his hands he does, and although it's the first person she's had to shoot, she kills the man when she sees a glint of silver in his palm and thinks it's a gun. It turns out to have been a crucifix and Cassie is never the same.
We learn that there were five waves to the attack by the Others:
1. The First Wave: an EMP is released on the Earth which kills all electronic devices; cars, cell phones, tv's, etc.
2. The Second Wave: a huge probe is dropped along the major fault lines in the ocean by the Others, causing tsunamis which obliterate any coastal cities/states/countries
3. The Third Wave: a virus is engineered by the Others to be carried by birds across the world as an airborne virus that causes human's insides to pretty much rot from the inside out and causes blood to pour from every orifice, even eyes.
After these 3 waves are complete, we find out that at this point the human population has dropped from 7 billion to an estimated 200,000
4. The Fourth Wave: the Others come to Earth disguised as humans to rid the world of the rest of the human population. They do this to turn human against human so no one knows who can be trusted, and while they wipe out the humans they find, people turn against each other and try to live solitary lives due to mistrust.
Throughout the book, Cassie flashes back to her previous life before the Others arrived (called the Arrival, go figure) and we learn that she lived a normal life and was in love with a boy who didn't know she existed named Ben Parish. She lived a normal life and had a loving family, but went through the usual teenage angst.
When the others came that all changed. Although her family tried to hide out in their homes while all of their neighbors fled to other places, her mom caught the 3rd wave virus and died. After she dies, her father tells her they have to leave and try to find someplace safer.
They end up in a camp where other survivors are living military style, armed to the teeth, while trying to band together. Their leader is a former military sargeant (?) named Hutchfield.
One day drones start appearing above the camp (this is at the beginning of the 4th wave), and everyone at camp is terrified, not knowing what the drones mean. A helicopter also shows up and the people have hope that the military has finally found them and will come save them, but the helicopter flies away after hovering over the camp a few moments.
That evening, military vehicles and some school buses do show up packed with kids. Corporal Vosch, the leader of this military group, meets with Hutchfield and tells him they will take the kids back to the military base not too far away (Wright-Patterson) and come back for the rest of the people afterwards. Sammy is put on the school bus with the rest of the kids but leaves Cassie his stuffed bear as a reminder of him until she gets to the base.
When Cassie and her father go back to the meeting room with Vosch and Hutchfield with the rest of the camp, her father gives her subtle hints that she should go look for Crisco. Cassie doesn't understand why he's telling her this, but she goes anyways with the accompaniment of a guard from Vosch's army.
They find Crisco in the ash pit (where people who have died of the virus have been burned) looking for jewelry and other valuable items. The guard with Cassie shoots Crisco as soon as they find him, but Cassie is able to kill the guard and hide by burying herself in the ashes of the pit before the other guards come.
When she thinks they are gone, she grabs Sammy's teddy bear and goes to the edge of camp to see if her dad or any others may still be alive. There she sees her dad crawling, having been shot. She starts to go to him but he sees her and motions that she stay hidden, and Cassie sees a pulsing light at the middle of camp, which turns out to be some kind of sonic wave that once it detonates kills everything within a few miles radius of the blast. When Cassie realizes it's a ticking time bomb she runs and jumps down a ravine into a pile of mud that shelters her from the blast.
In between this flashback scene, in present day Cassie is trying to get to the military base where her brother was taken to see if he is still alive. As she heads on her way there, she is shot by a Silencer (this is what Cassie calls the Others of the 4th wave, the human/aliens) and hides under a car while trying to think of a way to escape.
At this time, pov changes to a young soldier named Zombie who is at Wright-Patterson and has been infected with the virus of the 3rd wave and is close to death. While at a point where he is lucid, he sees that the base is being attacked and a soldier comes into his tent and tells him "they're here, they've been here the whole time inside of us", but not seeing what Cassie has already seen he has no idea what that means.
He awakens next in the hospital wing and the doctor explains what the soldier meant by showing him an ultrasound which shows thousands of long tendrils attached to the brain. The Others have apparently planted something in humans that takes over their minds and makes them Other but still look human.
She places an implant in his neck and tells him it's so they can keep track of the Wright-Patterson members who are still alive. She says 1 in 3 humans are now mutated like this and they have a program called Wonderland which they can hook up to his neck to see if he's "infested" and says they found the program on one of the infested's computer.
Wonderland also allows them to see his thoughts and memories as well so they know where best to place him in the ranks of the military (whether he is best as a fighter,medic,etc based on his personality traits).
She assures him that all infested inside the base have been dealt with and he just needs to focus on recovering, since his body is fighting the virus and he's getting better. She tells him she'll show him an infested and it turns out to be his bunkmate Chris. When he tries to defend Chris by saying Chris never tried to hurt him even when he was sick and vulnerable, she tells him all the infested seemed normal until they were activated. She places a button in front of him that says execute and tells him if he's going to be a soldier in this army (who it turns out Vosch is the general of ....hm) that he must be able to kill the enemy who doesn't look like an enemy. He hits the button.
Now we switch pov again to the Silencer (that's what we'll call him at this time since he doesn't have a name yet). He is the one who shot Cassie and he's waiting for her to come out from under the car so he can finish her off. It's revealed that he's been watching her this whole time, and although his task was to kill her he hasn't been able to make himself do it yet, even though he's killed other humans before.
During his chapters, we also learn how it came to be that the Others took human identities. When babies are still in the womb, the Others come to Earth and plant the tendril-thing in the baby. That baby is born with the Other always inside it, but is human until Awakened. Silencer reveals that the Awakening happened 4 years ago and he has been this human ever since, but of course had to still act human in order to wipe out the rest of humanity (the whole purpose of the 4th wave).
Now we're back to Cassie. She awakens in a house with a boy tending to her bullet wound. He introduces himself as Evan Walker. He nurses her back to health and they become close. He leaves at night time to go hunt but hardly ever comes back with anything so Cassie grows suspicious and tries to follow him. She can't keep up and when she turns to go back to the house he's there. He isn't angry, but tells her he goes to hunt just to keep his thoughts in order and to make him feel in control. She believes him and they live together for a while as she's recuperating. He eventually kisses her and tells her he's coming with her to go find her brother, since Sammy is her purpose and she is his.
Sammy's pov is next, and we find out that he has been taken to Wright-Patterson and placed in a military unit with older kids for training. Zombie is there, and it's revealed that Zombie is actually none other than Ben Parish. Zombie is the head of his squad and is assigned to be the one to teach Sammy (who's nickname is now Nugget) how to be a soldier.
On a side note, there is a section here where Vosch talks to Zombie and tells him a story about being given orders to kill everyone over 16 inside a camp right after the 4th wave started ( not sure how long ago the beginning of the 4th wave is supposed to have been at this point) since the military wasn't sure who was and who wasn't an enemy anymore.
So....is Vosch just a human taking orders from a higher up? Or is he an Other? If he's just a human how did he come to have the Eye (the sonic blast thing)? At this point we just don't know about him.
Now that we've established the first pov's of each of the characters, I will summarize the rest rather than going back and forth each time a POV changes.
Zombie and his squad are training to try to become fighters against the Others, and the top 4 squads are promoted at the end of training. His squad comes out on top with the help of the new squad member Ringer, a sharpshooter girl who is brought in after a squad member goes "Dorothy" , meaning he lost his marbles under all the stress and was put in the psych ward.
Zombie is promoted to sargeant and Vosch tells him his squad will be sent into the city to rid it of Others with the assistance of some handy dandy headsets that reveal infested as green and friendlies as just a shadowy color.
When they get to the city they immediately kill 3 Others but there's a 4th sniping them from a roof. Ringer insists they remove their trackers and Zombie thinks she's going Dorothy in the middle of battle but he does it because he knows that if she loses it she could kill them all as skilled as she is with a gun. Looking through the headset she immediately begins glowing green and they realize they haven't been shooting infested, but rather have been brainwashed into thinking their fellow humans were the enemy. Ringer says she has suspected but just now got a chance to prove it.
They go after the sniper and it turns out to be their former instructor. They kill him and Zombie vows to go back to the base to save Nugget. He has Ringer shoot him to buy him some time since he knows they'll put him on meds back at the base and won't be able to hook him up to Wonderland to see his thoughts for a while as he formulates a plan to get Nugget out.
He is picked up by the heli that dropped them off for their mission, and when he's taken back to base he tells Vosch everyone else turned against him when he tried to defend their instructor being there when everyone else said he was an Other. When Vosch asked why he defended him and went against the rest of the squad, Zombie says it's because he figured the instructor was there to take them out should anyone go Dorothy with the blood of first battle.
In the meantime, Cassie and Evan have decided to go after clues as to Sammy's location since they aren't even sure he's actually at the military base. They go to the camp where her dad and the others were killed looking for clues and are attacked. Evan easily dispatches all the kids (soldiers who are just like Zombie aka Ben and think they're Others) and Cassie realizes that although he claims to have been raised on a farm, his ninja skills and headshot sniping means he's something else. He is wounded in the fight and Cassie drags the truth out of him finally; that he is a Silencer who couldn't kill her because he has fallen in love with her. Although she doesn't know what to do about him now, she still proceeds with him to the base and poses as a kid seeking refuge while Evan waits for her outside the base in case anything goes wrong.
She gets inside and manages to find Sammy. When she starts to get away with him Zombie aka Ben shows up at the same time and they almost kill each other thinking they are both enemies but Sammy explains and the try to leave together.
When they are almost out Vosch catches them and takes them to an interrogation room. He is planning to kill Sammy unless Cassie tells him which of his kind betrayed them and told her how to infiltrate the base but she refuses. He pushes the button to kill Sammy but instead of "execute" the command prompt says "oops" and Vosch knows the Other working against them will shut down power to the base next so he tells the Silencer guards to keep them there and he'll be back.
Evan shows up by crawling through the ductwork and takes out the guards and he and Cassie have a joyful reunion. They run but he tells her to leave without him and she realizes he's going to blow up the base with the Eyes. She tries to convince him to come with them but time is short and he tells her he will find her.
Cassie, Ben, and Sammy take off and a get out just as explosions begin and drones begin dropping from the sky. She realizes Evan was able to do what he set out to do and the whole underground base has been blown to smithereens. The ground is giving way beneath them but a Humvee shows up and Ringer, Pound cake, and Dumbo (the other 2 surviving members of Ben's squad) show up and they make it to safety for now.
End of Book 1