There are no words to adequately describe how amazing this book is. All authors should take a page from Jen and realize that 
 this 
 is how you end a series! Sentinel picks up right where we left off in Apollyon, Alex, Aiden, and gang are trying to find a way to defeat Ares, all while trying to hold it together. This is seriously one of the craziest books I have ever read in regards to the emotional roller coaster the reader endures throughout reading. This novel is packed with action, adventure, and excitement, all while reminding us that these strong, brave characters are still human. It takes an amazing author to be able to do this, and Jen is an expect. 
 Alex and Aiden are stand out in this novel. Yes, the story has always revolved around them, but this amps up the romance between them. There are some of the sweetest moments I have ever read, which could only be pulled off by someone like Jen. If you weren't rooting for them before, you will be while reading this. I was worried that this book might focus too much on Alex feeling sorry for herself or having a hard time coping with the events that happened at the end of Apollyon, but no sirree! Alex comes back ready to fight to the end. She knows the consequences that could occur, but that doesn't stop her from going full throttle, balls to the wall, warrior girl. I was also worried that Aiden might resort to old ways and push Alex away. But have no fear, Aiden and Alex are closer than ever, and they stand by each other through thick and thin. 
 After the last book, I was really hating Seth, but honestly, after the ending of this book, I totally love Seth again. He is such a complex, crazy man that drives me insane, but trust me, your feelings will change toward him by the end of this novel. 
 Last but certainly not least, I must talk about the ending. The ending was so utterly heartbreaking at one point, and had me sobbing. So much happens that I wouldn't be able to keep this review spoiler free if I told you even basic details. So I'll say this, a lot of stuff goes down, and it's not all good. We lose people that are near and dear to us, and I'll tell you now, you will not be happy when one person dies. And just when you're heart is broken and you see no possible way for a happy ending, picture a little Jen Armentrout on your shoulder whispering, "Everything will work itself out." Because it does...in a humungous way. And I was literally cheering and smiling so big by the very last page. The ending is chock full of action, sadness, and tears, but also happiness and victory. Just be warned that you're heart and head will go through some serious emotions. 
 Overall, this is simply an amazing book, and an even more amazing end to the Covenant series. Jen is literally a book writing ninja that just amazes you with her skills time and time again. While I'm sad that this is the last book of Alex and Aiden, I will definitely be revisiting their world time and time again! Go get this book now! Happy reading :) 
 5+++++++ stars