Ally Carter never fails to reel me in with her amazing writing skills! I swear, I could read her novels all day. The characters, especially the four girls, Cammie, Bex, Liz, and Macy have grown up so much and have changed into very close friends and great spies. There's a ton of action scenes and suspense throughout the book so I never felt bored while reading and the romance between Cammie and Zach is still very strong and sweet but it has always taken the backseat and in United We Spy it's no different. 
 United We Spy is the final book. That's it. And even though I'm still unsure about how I felt about the ending, this is by far one of the best series I've ever been fortunate to read. Like any great series, it seems that you have to stumble upon them rather than look for them. I recommend this series to anyone who loves spy novels and are looking for a wild trip that will make you believe that you can be a spy yourself.