We open with a nostalgic flashback of twins Maggie and Milo as children, excitedly dressing up for Halloween with their father. Maggie reflects that perhaps the issues they face stem from their dad, as they were known as the “Gruesome Twosome.” Fast forward to present day, Milo, portrayed by Bill Hader, is blasting music in his apartment and staring at his reflection as he lays in a tub, only to tragically attempt suicide by slitting his wrists, leading to a grim scene where the water in the tub turns bloody.
Meanwhile, Maggie, played by Kristin Wiig, is struggling with her own demons. In a moment of despair, she holds a handful of pills as her phone rings, the cheerful theme song to Growing Pains marks the irony of her situation. When she visits her brother in the hospital—ten years since they last saw each other—a nurse hands her Milo’s suicide note which chillingly states, "To whom it may concern. See ya later." In response, she invites him to return to New York, but Milo hesitates, believing her offer is rooted in guilt and insisting he has pet goldfish to care for, to which Maggie counters that he can easily get new ones.
Upon arriving in New York, Milo meets Maggie’s husband, Lance, whose portrayal by Luke Wilson adds a quirky dynamic to the mix. He's a well-meaning man, though an unconventional match for Maggie, who is currently exploring new hobbies, including scuba diving lessons in preparation for their postponed honeymoon in Hawaii.
As the story unfolds, Milo finds himself exploring the city, running into Rich at a bookstore, and later trying to navigate a gay bar only to realize it’s a dyke night. After a drunken night filled with stories of mishaps, he begins to face the realities of his past. The awkward family dynamics are further complicated when their free-spirited mother makes an appearance, revealing her detachment from the family.
In subsequent days, Maggie's interactions with Milo lead to deep discussions about motherhood and relationships. When she tries to bond with a scuba instructor named Billy, played by Boyd Holbrook, she finds herself entangled in a brief affair, highlighting her own struggle with fidelity. Milo and Maggie's conversations become a blend of levity and emotional gravity as they tackle life’s profound questions and the weight of their family history, with Milo jesting about Maggie’s potential as a mother while also diving into their shared past filled with pain and revelation.
As Milo reconnects with Rich and explores his childhood trauma, Maggie grapples with her own choices—ultimately revealing that she’s been taking birth control for reasons tied both to her personal freedom and her marital infidelity. Their dynamic postures between humor and sorrow, evidenced by a humorous exchange where Milo candidly addresses the societal expectations imposed on them.
Tensions arise, culminating in a dramatic confrontation after a Halloween night meant for bonding descends into chaos as truths are brought to light. The siblings navigate the aftermath of dark secrets and the instability of their shared history, which ultimately leads to a near-tragic event in a pool where Maggie attempts to drown herself.
The narrative crescendos, and just as tragedy seems inevitable, Milo jumps in to save her, resulting in a poignant moment of unity and reflection. This act sparks a new beginning, symbolized by the goldfish Maggie buys for her brother—an emblem of their commitment to healing and rebuilding their fractured lives.
