A suspenseful young adult mystery thriller by Karen M. McManus centered on a wealthy family's darkest secrets.

Milly, Aubrey, and Jonah Story are cousins who have never met one another. Years ago, their mysterious grandmother, Mildred Story, abruptly disinherited all three of her children without explanation, cutting the entire family out of her life. None of the cousins knows why.

When the teenagers unexpectedly receive invitations to spend the summer working at their grandmother's luxurious island resort, they see it as an opportunity to uncover the truth behind the family's estrangement—and perhaps reclaim their inheritance.

As they investigate the Story family's past, they discover hidden relationships, betrayals, lies, and decades-old secrets that someone has gone to great lengths to conceal. Told through multiple timelines and perspectives, the novel gradually reveals what really happened all those years ago, building toward a shocking final twist that changes everything the cousins believed about their family.

Combining family drama, mystery, and psychological suspense, The Cousins is a clever standalone thriller with rich character development and a tightly woven plot.