There are some mystery novels that you can easily predict, and some will leave you speechless because you are caught off guard with the twist. 
 Don't Look Back is a light mystery novel with a bit of romance and it's my first Jennifer L. Armentrout book that I've read. I am captivated with the twist and I had fun trying to figure out of how this will end. On some parts, I find it a little predictable and somehow I guessed it right. 
 I listed my theories and whereabouts but I had difficulties on finding out who is the suspect. I suspected 4 people: 
 (view spoiler)[1. Del - I knew right at the beginning he hooked up with Cassie, he has a great potential as a suspect because his relationship with Samantha was destroyed and he regret it. I think he wants Cassie out of their lives. His looks can be deceiving you know. 
 2. Scott- He doesn't like Cassie at all, because it changes Samantha's attitude (from a good girl to a bitch) 
 3. Carson - I don't know. I was caught off guard with that freaking black cap and I thought he is the shadowed man (Samantha's stalker) 
 4. Samantha's father - there was something odd about him, I have doubts that he is the suspect but more like 50/50. When Samantha went to their vacation house, she noticed cigarette butts along the way as she tries to recall her memories. Her dad smokes cigarette, then on. I've been suspicious and pretty much becomes evasive at some points. (hide spoiler)] 
 Great mystery. Prepare for some surprises. I'm happy that somehow I get it right. I'm sure be looking forward to read more of J.L.A's books.