The Woman in the Window by A.J. Finn

Anna Fox lives alone—a recluse in her New York City home, unable to venture outside. She spends her day drinking wine (maybe too much), watching old movies, recalling happier times... and spying on her neighbors.
Then the Russells move into the house across the way: a father, a mother, their teenage son. The perfect family. But when Anna, gazing out her window one night, sees something she shouldn’t, her world begins to crumble—and its shocking secrets are laid bare.
What is real? What is imagined? Who is in danger? Who is in control? In this diabolically gripping thriller, no one—and nothing—is what it seems.