For the Last Time by Heidi Perks

Internationally bestselling author of the "gripping" (Lisa Jewell) Three Perfect Liars, Heidi Perks is back with a thrilling new novel.
Dark secrets are revealed when a therapist becomes obsessed with her troubled new patients, for fans of Alex Michaelides and The Golden Couple.
When Erin and Will walk into Maggie's office for a marriage counseling session, Maggie believes they are an ordinary couple with ordinary problems: communication, intimacy, the usual. But as Maggie struggles to get the couple to open up about what brought them here, she begins to sense that not all is as it seems.
When Erin mentions something connected to Maggie's past that she couldn't possibly know, Maggie is disturbed and confused. Why does Erin know anything about Maggie's long-missing sister? Erin is connected to her somehow, and Maggie is no longer trying to fix the couple's marriage–she's trying to uncover her own truth. Maggie knows her code of ethics as a therapist should immediately stop her working with this couple, but she's desperate for answers about her sister's disappearance, and she can't resist using her position to delve deeper into Erin's memories and what she might know. Erin and Will might not be what they seem–but neither is Maggie.
This dual-perspective psychological thriller will keep readers turning pages until every last secret comes to light.