Artifice by Christy Barritt

Three missing teens. One questionable school. Zero room for error.

When the teenage son of a prominent Boston family vanishes from Lighthouse Harbor—an exclusive institution for troubled teens—private investigator Olive Sterling is called to find him.
Posing as a wealthy benefactor, Olive infiltrates the school. But something sinister lurks within. Other students have gone missing. Each time a student disappears, the administrators label them runaways. But Olive doesn’t buy it. Strange behavior from the staff, whispers of experimental treatments, and a suspicious death all point to a dangerous conspiracy.
Complicating matters is Simon Long, an education consultant whose penetrating questions and convenient timing make Olive question his true motives. Their undeniable attraction only adds to her confusion. Is he an ally in her investigation or someone with a hidden agenda of his own?

With time running out, Olive must face harrowing cliffs of deception to uncover the truth and save the students before another life is lost.