Dramas like
Nine Puzzles

Same writer, and the same trust in a procedural's own rules. Lee Eun Mi wrote both, and both build a case system and then respect it: a 1986 detective chasing a serial killer falls into 2017, and for seven episodes it is nearly as good as Signal. Difference: Tunnel gets careless in its back half, where this holds its shape and simply lands smaller than it promised.

Hooks early Episode 1. A 1986 detective lands in 2017 inside the first twenty minutes.

Two policemen who each believe the other is a murderer, and neither is wrong about how far the other will go. The ambiguity is maintained by writing rather than by withholding information, which is the hardest version of this trick. Difference: Beyond Evil is a character study with a plot that loops, where this is a puzzle box with a solution waiting at the end.

Slow start Episode 3, the point at which you stop trusting both leads at once.

Two specialists circling each other for eight episodes on the same platform. A mentor and a protege in neurosurgery, more interested in the ethics of genius than in the surgeries, with Park Eun Bin delivering and the direction keeping the temperature high. Difference: Hyper Knife has no case to solve and no investigation, so the suspicion is professional rather than criminal.

Slow start Episode 3, when the mentor and the protege stop circling and start operating on each other, figuratively and otherwise. Episode 4 is the peak.

Structure as the trick, on the same platform and at the same length. A present-day siege cut against a childhood of deniable preparation, so every flashback lands as ammunition rather than as context. Kim Hye Jun carries it. Difference: A Shop for Killers is an action series and this is an investigation, so the pleasure there is the reveal of a skill rather than of a name.

Hooks early Episode 1. The uncle is dead, the house is under attack, and the flashback structure starts working straight away.

Real structural ambition on a twenty-episode thriller. An 8.9 from 45,000 ratings with per-episode scores that never drop below 8.4, and Lee Seung Gi doing something extremely difficult with posture as much as face. Difference: Mouse is badly overlong, where this is exactly as long as its idea, and the gore in Mouse is far less clinical.

Hooks early Episode 2, once the killer and the two men chasing him are locked into the same story.

A detective compromised by his own case, at a similar length. A narcotics investigator is forcibly addicted to the drug he is chasing, which gives fourteen episodes a physical urgency most procedurals never find. Ji Sung makes the withdrawal real. Difference: Connection puts the damage in the lead's body, where this puts the suspicion on the profiler's record.

Hooks early Episode 1. The forced addiction happens straight away and the countdown starts with it.