It’s 1964 in Alderney, the northernmost Channel Island in the U.K., and it’s a time of societal change with a new international phone line and changing attitudes about female roles in the workplace. Agnes, 24, works alone as a switchboard operator in the telephone operator exchange. She passes the time listening to phone conversations while connecting people. When she receives a distressing call from a woman who suffers from dementia suggesting a kidnapping, Agnes alerts the police and uses her powers of deduction and local knowledge to help the police track the abduction. But things take a turn for the worse when she realizes everything is not as it seems. As more callers share information, Agnes deduces that Harold, a local workman, is the kidnapper. She assists the police in tracking him, but the situation becomes complex. Eventually, the kidnapped woman is found, but Harold now contemplates suicide. Drawing from her own experiences, Agnes attempts to talk him down.