From the #1 New York Times bestselling author of Alex & Eliza comes a return to adult fiction, centered around a mysterious woman's birthday celebration—and what it reveals about her past.

Ellie de Florent-Stinson is celebrating her fortieth birthday with a grand celebration in her fabulous house in Palm Springs.

At forty, it appears Ellie has everything she ever wanted: a handsome husband; an accomplished, college-age stepdaughter; a beautiful ten-year-old girl; two adorable and rambunctious six-year-old twin boys; lush, well-appointed homes in Los Angeles, Park City, and Palm Springs; a thriving career as a well-known fashion designer of casual women's wear; and a glamorous circle of friends.

Except everything is not quite as perfect as it looks on the outside—Ellie is keeping many secrets. This isn’t the first of her birthday parties that hasn't gone as planned. Something happened on the night of her sweet sixteenth. Something she’s tried hard to forget.

But hiding the skeletons of her past comes at a cost, and all of Ellie’s secrets come to light on the night of her fabulous birthday party in the desert—where everyone who matters in her life shows up, invited or not. Old and new, friends and frenemies, stepdaughters and business partners, ex-wives and ex-husbands congregate, and the glittering facade of her life crumbles in one eventful night.

Beautifully paced and full of surprises, The Birthday Girl is an enthralling tale of a life lived in shadow, and its unavoidable consequences.