23-year-old Owen works as a sound engineer at a student union bar at the fictional Manchester City University. One night he meets a girl and finds himself falling for her. Abruptly, the girl leaves, giving him her first name, "Emily", and her phone number. The next morning, Owen tries to text Emily, only to find that she missed a digit in her number. Mocked by his older brother Matt, Owen sets about finding Emily.

Meanwhile, third-year psychology American student Emily Raine – a different Emily to the one Owen met – is under pressure to finish her thesis, a good mark on which will grant her allow her to retain her visa status whilst also giving her a prestigious job in Manchester. Her hypothesis is that love is a kind of madness and a vestigial evolutionary impulse. Owen comes to her class seeking Emily and when she meets him and learns of his search, she decides he is the perfect case study to base her thesis around.

Despite ethical concerns from her professor and flatmates, Emily befriends Owen under the pretense of helping him find Emily, leading to a series of misadventures. When Owen hits a brick wall while searching for Emily, she encourages him to continue and even goes to far as to provide him with a list of email address for every Emily on campus. Owen proceeds at her urging to anonymously email every Emily registered at the university, leading to controversy. Student Union President Emily Thewlis, an outspoken wannabe feminist, begins a campaign against the anonymous emailer, known as "Email Guy". Owen shocked but trying to do right and redeem himself agrees to go on a student podcast to speak about his quest to find Emily. During the interviews Owen admits that he hacked the email server to get the email list (to protect Emily Raine). Just as the interview is almost a disaster, Owen performs a song he wrote for the missing Emily, which unexpectedly goes viral.