Under this red rock / Mindy McGinnins.

Enhanced descriptions from Syndetics:

From award-winning author Mindy McGinnis comes a mesmerizing YA psychological mystery following a teen girl who is grappling with the death of her brother as she starts a new job in the caverns of Ohio--only to become the number one suspect in her coworker's murder. Perfect for fans of Courtney Summers and Kathleen Glasgow.

Neely's monsters don't always follow her rules, so when the little girl under her bed, the man in her closet, and the disembodied voice that shadows her every move become louder, she knows she's in trouble. With a history of mental illness in her family and the suicide of her older brother heavy on her mind, Neely takes a job as a tour guide in the one place her monsters can't follow--the caverns. There . . . she meets Mila. Mila is everything Neely isn't--beautiful, strong, and confident. As the two become closer, Neely's innocent crush grows into something more. When a midnight staff party exposes Neely to drugs, she follows Mila's lead . . . only to have her hallucinations escalate.

When Mila is found brutally murdered in the caverns, Neely has to admit that her memories of that night are vague at best. With her monsters now out in the open and her grip on reality slipping, Neely must figure out who killed Mila . . . and face the possibility that it might have been her.

Reviews provided by Syndetics

Publishers Weekly Review

Via a horror-tinged psychological thriller, McGinnis (A Long Stretch of Bad Days) uses the lens of a whip-smart teen from a family with a history of mental illness to sensitively explore relevant themes. After gay 16-year-old Neely Hawtrey's mother dies in a car accident, her older brother Lance dies by suicide, and her father abandons her, Neely and her three secret monsters--a girl who lives under her bed, a strange man who inhabits her closet, and an annoying presence called Shitbird Man--move in with her grandparents in East Independence, Ohio. Neely is soon hired at a local cavern tourist attraction, where she crushes on her hot, tall, blond coworker Mila Minter, an English major at Ohio State University. Neely loves her job; hanging out with Mila and the fact that her monsters can't follow her underground allow Neely to briefly forget about her problems and her past. She's even started developing better coping mechanisms to manage her hallucinations and has befriended other cavern workers--but then a terrible crime occurs, destroying her carefully constructed reality. Neely is an acerbic protagonist whom readers will love and empathize with as she endeavors to regain control of her own life. Striking a careful balance of dry humor and occasionally harrowing depictions of Neely's mental health challenges, McGinnis delivers a compassionate and gripping read. Main characters read as white. Ages 14--up. Agent: Adriann Ranta Zurhellen, Folio Literary. (Mar.)

Booklist Review

Sixteen-year-old Neely's life is lonely, despite her "monsters"--a man she sees in the closet and a little girl under the bed, among others. Neely's parents are gone, and her brother, Lance, has died by suicide, leaving Neely alone to protect their grandparents from her mental illness and the fact that she's a lesbian. A summer job at an underground cave system where her monsters cannot follow brings new friends and renewed resolve but still can't prevent Neely's brewing internal storm. Grief clouds an already tenuous grasp on reality, and her mental illness begins manifesting in ways that Neely can no longer control or even remember. When her beautiful new crush, Mila, dies a gruesome, mysterious death, a dream come true becomes another living nightmare for Neely, who can't remember what really happened that night. Tackling a sensitive subject that easily could have veered into sensationalism, McGinnis cleverly shapes a tender examination of mental illness, grief, and love that still contains her characteristic dry wit and deeply disturbing imagery. While Neely's condition may be rare, the feelings of isolation and burdensomeness she experiences are not, and a realistically open ending leaves room for Neely's condition to improve without tying things up too neatly.

Kirkus Book Review

In an insular Ohio town, a young woman struggles with family trauma and experiences hallucinations that she keeps secret. Sixteen-year-old Neely, like her dad and older brother, Lance, who is now dead by suicide, can hear voices. Neely's mother died in a car accident many years ago, and later her dad left, leaving Neely living with her touchingly supportive but somewhat repressed grandparents. A longtime fan of the large cave system that's a tourist attraction in her town, Neely snags a job working there for the summer. Neely, who's gay but not out to many people, quickly falls for beautiful, smart Mila, who runs tours of the caves. When a shockingly horrific death occurs in one of the caves after Neely tries weed for the first time at an employee after-party and experiences what seems like a psychotic break, she fears she may be responsible. This gritty and sometimes gruesome thriller thrums with gripping menace, especially as Neely's brother's only friend, Brian, alleges that Lance was sharing incel-like posts on an anonymous internet site. Neely's frank, self-deprecating inner monologue is often bitingly funny, providing balance to the grim subject matter. Though they're portrayed with nuance, Neely's hallucinations sometimes seem to move with the plotting, which, given the unpredictable nature of serious mental illness, can make this element feel too convenient. All the main characters read as white. A propulsive, unpredictable, and troubling thriller. (Thriller. 14-18) Copyright (c) Kirkus Reviews, used with permission.