Oh Jun-yeong never has to break into anything. Lee Na-mi (Chun Woo-hee) leaves her phone on a bus, he picks it up, and a voice disguised by a fake app tells her where to collect it the next day. That is the whole hook of Unlocked, and it is a good one. The trouble starts when the film has to decide what to do with it.

Kim Tae-joon’s debut is a remake of the 2018 Japanese film Stolen Identity, and it plays like one: competent, tidy, rarely surprising. The tech-savvy villain, the isolated heroine and the police always one step behind are all here. Nothing is wrong with those ingredients. The film just seldom rearranges them into anything you haven’t already seen.

Chun Woo-hee has the harder job. Na-mi markets jelly drinks for a start-up and helps out at her father’s cafe, so she is busy, a little overworked and entirely believable as someone who would hand her password to a stranger. The repair shop scene, where a masked man fixes her cracked screen and quietly asks for the code, is the best thing she does, because she plays it as plain politeness. Later, once the fear has to carry the film, her reactions sometimes go flat. The script hurries her from one humiliation to the next and gives her little room to react.

Yim Si-wan is the film’s best asset. His Jun-yeong is friendly, attentive and always turning up at the right moment, because he has read her life on her own phone and stages each meeting. He is pleasant enough that the suspicion of Na-mi’s father, Seung-woo (Park Ho-san), looks like the only sane response, which is exactly why the film has to lock the old man away. Yim never overplays the menace. The smile does most of the work.

The middle stretch is the film at its sharpest, and it contains almost no violence. Jun-yeong leaks company information through Na-mi’s social accounts and she loses her job. He then intercepts her message to a digital safety expert and answers it himself. He convinces her that her best friend Eun-joo (Kim Ye-won) is behind the hack. Within days she has no work, no friend and no one to believe her, and the police tell her to bring evidence before they will act. Nobody breaks down a door here. A woman is simply shut out of her own life, one ordinary app at a time.

The police thread is less successful. Detective Woo Ji-man (Kim Hie-won) is looking into a body found on a remote mountain, and the clues lead him to Jun-yeong, the son he has not seen in ten years. It is a strong idea, but it arrives as a separate film stitched alongside the first, and each cut to it drains the pressure that Na-mi’s scenes have built. Ji-man and his partner Jeong-ho (Jeon Jin-oh) also weaken the trap set at her apartment. They watch Jun-yeong walk up to the building, do not recognise him and let him leave. The story needs that to happen, but it is hard to believe.

The last act moves to Seung-woo’s house, where Jun-yeong forces Na-mi into a choice that is cruel even by the standards of the genre. The revelation that follows, that this man took the identity of Ji-man’s real son, his first victim, gives the detective plot the weight it lacked. It arrives late, though, and the film does not let it breathe.

Unlocked reached Netflix on 17 February 2023, and it suits the format: easy to start, easy to follow, a little too long in the middle. The premise is sharper than the execution, and the performances, Yim’s above all, are better than the script they serve. It is a competent thriller with one excellent stretch and too many familiar beats around it.