The Pact by Sharon Bolton is a well paced, exceptionally fun thriller. It uses the trope of an old group of friends with a big secret and twists and plays with that to great effect. When they were 18, Amber, Talitha, Zav, Dan, Felix and Megan all spent the summer together before exams. They developed a dangerous routine, and when it comes down to it Megan takes the fall for all of them. With one promise, that they will all owe her any favor she demands when she gets out of prison. 

Twenty years later, Megan is finally released and the torturous requests begin. The friends are beside themselves with fear and must devise a plan to escape Megan's demands. Honestly, you don't need to know anything else going in. This is such a fun ride, and I don't mean that as a pun but it does work. 

I'm an avid thriller reader and this satisfied me, kept me engaged, and I devoured it quickly. I was pleased with the twists and the delightfully unsettling ending. Highly, highly recommend.