No One Can Know by Kate Alice Marshall

Three sisters, two murders, and too many secrets to count.

Fourteen years ago, the Palmer sisters—Emma, Juliette, and Daphne—left their home in Arden Hills and never returned. But when Emma discovers she’s pregnant and her husband loses his job, she has no option but to return to the house that she and her estranged sisters still own . . . and where their parents were murdered.
Emma has never told anyone what she saw the night her parents died, even when she became the prime suspect. But her presence in the house threatens to uncover secrets that have stayed hidden for years, and the sisters are drawn together once again. As they face their memories of the past, rivalries restart, connections are forged, and, for the first time, Emma starts to ask questions about what really happened that night.
The more Emma learns, the more riddles emerge. And Emma begins to wonder just what her siblings will do to keep the past buried, and whether she did the right thing staying quiet about what was whispered that night: “No one can know.”