Marlo (Theron) just had her third child and is overwhelmed with taking care of the baby, as well as her two older kids. Her brother Craig (Duplass) offers a solution: a night nanny that he would pay for himself. Enter Tully (Davis), who is there to "take care" of Marlo and her kids.
This film provides examples of:
- Ambiguous Disorder: While not explicitly named, Jonah's mannerisms, such as constant stimming and sensitivity to sound, heavily imply that he has Autism. Also possibly Marlo, given The Reveal that she vividly hallucinated Tully as a coping method due to her extreme exhaustion and stress.
- Ambiguously Bi: Marlo is in a stable marriage with Drew, but while drunk she mention having been "in love with" her former roommate Violet.
- Book-Ends: The film opens with Marlo brushing Jonah's skin as a means to soothe him, and at the end of the film, she goes to do so again, but Jonah decides he doesn't need to be brushed.
- A Boy, a Girl, and a Baby Family: Marlo has a daughter, Sarah, a son, Jonah, and another baby on the way, who turns out to be a girl named Mia.
- Casual Kink: Marlo finds out Drew has something of a fetish for the waitress outfits of the 50's/60's.
- Cluster F-Bomb: Marlo lets a few loose when speaking to the principal of Sarah and Jonah's school since Marlo thinks they are singling Jonah out because of his autism.
- Foreshadowing: Tully mentions to Marlo that she's not as young as she looks.
- Imaginary Friend: Tully turns out to be nothing but a product of Marlo's imagination.
- Really Gets Around: Tully mentions to Marlo that her roommate is upset that she brings lots of guys home.
- The Reveal: Tully never existed. She was a product of Marlo's sleep deprivation and exhaustion, specifically a projection of her own younger self, and everything we saw them doing was just Marlo acting alone.
- Shout-Out: Marlo asks Tully what she's been doing, and she responds "Same thing I do every night... try to take over the world!"
- A Threesome Is Hot: Zig-Zagged. Drew requires very little convincing to have sex with the younger nanny he's never met while his wife watches. His quick acceptance of this too-good-to-be-true scenario makes sense when we find out it was just him and Marlo.
- Triple Shifter: Deconstructed. Marlo is The Insomniac and it starts to affect her sanity, which becomes a vicious cycle when she develops a split personality as her own night nanny, and seemingly hardly ever sleeps. Gets to the point that she falls asleep at the wheel and crashes her car.
- Wham Line: "What's her maiden name?" Tully.