With similar supernatural/fantasy themes:
* The Raven Cycle by Maggie Stiefvater: Stiefvater's other series, featuring a group of boys searching for a Welsh king and a mysterious girl who might be connected to the legend.
* A Court of Thorns and Roses by Sarah J. Maas: A young woman is taken to a magical land and finds herself caught in a dangerous game of power and love.
* Daughter of Smoke & Bone by Laini Taylor: A young woman falls in love with an angel, but their relationship is forbidden and dangerous.
* The Cruel Prince by Holly Black: A human girl finds herself in a magical world ruled by faeries, where she must navigate treacherous politics and dangerous relationships.
* The Night Circus by Erin Morgenstern: A magical competition between two young illusionists, where the stakes are high and the romance is forbidden.
With similar romance themes:
* The Love Hypothesis by Ali Hazelwood: A fake relationship between a scientist and a professor quickly turns real.
* Red, White & Royal Blue by Casey McQuiston: A romance between the First Son of the United States and a British Prince.
* The Kiss Quotient by Helen Hoang: A woman with autism hires an escort to help her learn about intimacy.
* The Hating Game by Sally Thorne: A workplace rivalry turns into a steamy romance.
* To All the Boys I've Loved Before by Jenny Han: A high school girl's secret letters to her crushes get sent out, leading to unexpected consequences.
With similar "mystery" elements:
* The Girl on the Train by Paula Hawkins: A woman becomes obsessed with a couple she sees from her train window and gets caught up in their lives.
* Gone Girl by Gillian Flynn: A husband becomes the prime suspect in his wife's disappearance, but the truth is far more complex.
* The Silent Patient by Alex Michaelides: A psychotherapist becomes obsessed with his patient, a woman who has been silent for six years since killing her husband.
Ultimately, the best book for you will depend on your personal preferences. I recommend checking out reviews and summaries of these books to see which ones pique your interest. You can also search for "books similar to Shiver" on Goodreads or other book-reviewing websites. Happy reading!