After the End by Bonnie Dee (2010). A group of strangers fight to survive the zombie apocalypse, which hits while they're riding the NYC subway. Told through the eyes of Ari, home on leave after Army basic training, and Lila, a college student and pacifist. See what happens as they experience the very earliest days of fighting to survive, loss, and adding others to the group.
Swapped by Brynn Paulin (2015). Mallory and her husband Tom attend a party held by Jayson, Tom's boss. Mallory thinks this is the usual career networking, support her spouse situation. Imagine her surprise not only to find a spouse swap party in full effect, but also to learn that Tom brought her there for Jayson. Graphic scenes, yet also surprisingly romantic.
Powers of Darkness: The Lost Version of Dracula by Bram Stoker and Valdimar Asmundsson (1901 in Iceland, 2017 English translation). A shorter, more graphic version of the Dracula tale that I highly recommend for anyone who appreciates vampire stories.
Dr. Franklin's Island by Ann Halam (2007). Maya read this book at school, and she said she thought I would "like" (in the creepy, fascinating sense) it, too. Yep! Three British teens are the only survivors when their plane crashes on an island during their journey to Ecuador. Unfortunately, this is Dr. Franklin's island, and he's only too thrilled to use healthy teens in his genetic engineering experiments. Think The Island of Dr. Moreau by H.G. Wells, and you have a good idea of what happens.