While busking in Grand Central Terminal, Nick Vaughan (Chris Evans) sees a woman running by to catch the 1:30a.m train to Boston dropping and breaking her phone. She misses the train and is forced to return. Nick returns the phone to the woman, Brooke (Alice Eve). When he finds her standing outside the terminal she confesses that she has just been robbed and is trapped in the city. He offers to pay for a cab to take her toBoston but his credit cards are declined. When he tries to call a friend to come loan him the money he finds his phone has died. Nick offers to try to pay for a room for Brooke to stay in overnight, but she insists that she needs to return home before the morning.
Nick decides to help Brooke find her missing purse. The two are able to track it down at a sweatshop that deals in stolen purses but for his efforts to retrieve the purse Nick is punched in the face. The two try and go to Nick’s friend’s wedding in order to find his friend to loan him money and instead end up at an event where they are mistaken for members of the band. Nick and Brooke perform My Funny Valentine before being forced to flee when the real band shows up. After their last ditch attempt to get a bus to Boston fails as they don’t have enough money, Brooke borrows a man’s phone and calls a friend whom she begs to go to her house and retrieve a letter she has left for her husband that she does not want him to read.
Elated that her problem is now solved Brooke offers to go to Nick’s friend’s wedding and pretend to be his girlfriend in front of his ex, Hannah. At the reception Nick sees Hannah but after being introduced to her new boyfriend he leaves abruptly. Outside Nick tells Brooke that he hadn’t seen Hannah in six years since he went to propose to her and she broke up with him. At Brooke’s insistence, Nick goes back to speak to Hannah to see if he still has a shot with her. Instead he discovers that she’s pregnant and that he has no chance with her. Wandering around the city the two find a psychic who is still open. After he reads her future he allows Brooke to use her phone where her friend tells her that she was unable to get into her home and retrieve the letter.
After they leave the psychic’s place, Brooke reveals to Nick that she had discovered that her husband was cheating on her. Though he ended the relationship she discovered that he was going to see his mistress again. Devastated, she wrote him a letter ending the marriage and went to New York for work. However during her trip she received a phone call from her husband saying he was coming home early and realized that he had ended the relationship for good.
At a restaurant Nick tells Brooke that her husband will most likely understand that what he did was wrong and that if he doesn’t, that’s that. They then go to Nick’s friend’s hotel that he’s staying at. Together they write on the back of paintings in the room (a reference to an earlier encounter with a painting with erotic writing on the back of it). They then share a kiss and reflect on their night.
In the morning they return to the train station where they are about to part. Suddenly, Nick picks up a phone from a phone booth and, like an earlier joke, uses it as a “time machine” and pretends to call himself saying that he will meet a woman that he should stay with for the night. They share one last kiss and finally depart. On her way home, Brooke finds a guest service paper that she and Nick filled out at the hotel. On the bottom it says “turn over.” She turns the paper over and smiles at what she reads, though the message itself was left ambiguous at the end.