I always love a good thriller. I listened to the audio book of this one while doing other mindless tasks. It was a good balance between the heartwarming parts and unfortunate tragedy. There are some descriptions in the book that wouldn't be good for a younger audience, so I would say over the age of 16-17 for this one, but definitely a recommended read.
The main character, Ella, witnesses two young girls on the train flirting with two men out of prison. She's on high alert but ultimately decides to not do anything. Sadly, the next day she sees that one of the girls, Anna, is missing.
A year goes by and Anna is still not home. Ella feels horrible for the role she played in the disappearance. On top of it all, she's getting mysterious threatening letters centered around Anna's disappearance.
Eventually, it's revealed that Anna's best friend, Sarah, hasn't been entirely honest and that Sarah's own parents have got some dirt that's been swept under the rug. "Someone knows where Anna is—and they’re not telling. But they are watching Ella." - Direct quote from cover copy
If you like a thriller then is a must-read. Below is the link to find it on Amazon. It's available on Kindle Unlimited or you can buy it on Kindle for $1.99.