Finally, the ending to the young adult scifi series “The 5th Wave,” is out. The author, Rick Yancey, has kept readers wondering what the true nature of the 5th wave will be. The first few “waves” have decimated the Earth’s population killing 7.5 billion people. The very first wave was a massive EMP, electromagnetic pulse that killed all electronics. Planes fell from the skies, cars lost power, all electricity shut down. The next wave was when “The Others,” the aliens, dropped some kind of huge rod onto one of Earth’s fault lines resulting in earthquakes and huge tsunamis that destroyed all Earth’s coastlines and those who lived there. The 4th wave consisted of humans called Silencers, a group of humans who while fetuses were downloaded with alien memories and technology. They didn’t know about it until they turned 13. That’s when they began to kill other humans. Other humans know about the Silencers, but because they look and act just like other humans, they are virtually impossible to detect until they start killing people.

Cassie and her group of allies — some are friends and some are not — are trying to survive. Cassie and her brother Sam survived the first waves, and she is with him in this last book, along with former crush Ben Parish (also known as Zombie), and Evan, who is a Silencer but who fell in love with Cassie and will do anything to protect her. Others include Ringer, Poundcake, and Dumbo (names they were given at the military “camp” that trains children to be killers of other humans).

The aliens who caused this devastation have been watching Earth for ten thousand years and have watched the gradual deterioration of the planet under mankind’s less-than-stellar stewardship. Finally, in order to save the planet, they create a series of events designed to decimate Earth’s population. One of the most fanatic of the alien followers is Colonel Vosch, the Nazi-like, unfeeling, sadistic person in charge of the military camp where Cassie and her group each have spent some time. Eventually, every character in the book meets up with him.

For those who read the first two books as soon as they were published, it’s probably better to reread those books before attempting the third and final book. Yancey creates a group of characters and a plot and subplots that are complicated and interwoven. The only way to really remember and know what is going on is to have recently read (or at least skimmed) the first two books.

Yancey’s writing is just as solid and descriptive as in the first two books. The story is told all in first person narrative from several different points of view. It allows the reader to understand the characters’ motivations and actions. What Yancey does beautifully is reveal the human condition. Some of us take whatever we can get in times of trouble and, like Vosch, use power to ensure survival at all costs. Other humans realize that individual survival at any cost is not always the most courageous option. When humanity is in danger, what is one life worth?

None of the characters is perfect. Cassie kills an unarmed soldier in the first book, but this incident and the reason she killed him are replayed throughout the series. She thinks of those issues when she is forced to make difficult choices. What is one life worth? A valid question and one that is worthy of discussion and reflection.

Yancey makes a statement here about the fact that when hundreds or thousands of people die, we can somehow become inured to those deaths. But when one person dies in front of us — it can be a revelation. 7.5 billion people is an unimaginable number, but a little girl with a bomb in her throat is just one person. What is her life worth? What is the value of the lives of the children who are brainwashed into carrying bombs of their own and detonating them? That really happens in our world. Those questions are certainly thought-provoking; and young adult readers should be carefully and painstakingly considering them.

What finally vanquishes the aliens and their evil plan to exterminate the human race? No spoilers here, but it’s a human emotion that resonates in each book. It’s the strongest human emotion there is.

Please note: This review is based on the final hardcover book provided by the publisher, Putnam, for review purposes.