Spoiler warning: This guide reveals how Heiji discovers Conan’s identity and what changes between them afterward.
Heiji learns that Conan is Shinichi near the end of Japanese episode 58. In the manga, the decisive scene is Volume 13, File 1—overall File 121. The case begins one episode, or several manga chapters, earlier, so the start of the mystery and the actual reveal have different reference points.
Heiji does not simply recognize an old rival in a smaller body. He watches Conan, tests his suspicions, and catches him using the very method that normally keeps his identity hidden. That sequence turns the reveal into a second detective story running beneath the murder case.
Where to watch or read Heiji’s discovery
| What you want to see | Anime: Japanese numbering | Manga |
|---|---|---|
| The complete Sherlock Holmes fan gathering case | Episodes 57–58 | Volume 12, Files 7–10, through Volume 13, File 1; overall Files 117–121 |
| Heiji confirms Conan’s identity | Near the end of episode 58 | Volume 13, File 1; overall File 121 |
| Their earlier meeting, before Heiji knows | Episodes 48–49 | Volume 10, the diplomat case |
The anime numbers above follow the original Japanese broadcast. Start with episode 57 for the buildup: Conan, Heiji, and the other guests attend a gathering for Sherlock Holmes enthusiasts, and a quiz event gives way to a murder investigation.
In the manga, Heiji’s doubts become particularly strong by Volume 12, File 10. The following chapter supplies the confirmation. Reading across the volume break lets the murder investigation and Heiji’s investigation of Conan arrive at their answers together.
How Heiji works out that Conan is Shinichi
Conan’s deductions give Heiji a reason to look closer
Conan reads the crime scene too quickly and takes too active a part in the investigation to pass comfortably as an ordinary elementary school child. Around adults, he can disguise a deduction as an innocent hint. Heiji is another high school detective, and he notices the reasoning behind those hints.
He also has a useful point of comparison: he has already exchanged deductions with Shinichi. Conan’s speed and approach may remind him of that earlier encounter. That resemblance supports a suspicion; it does not yet prove that Conan and Shinichi are the same person.
Heiji’s apparent confusion forces Conan to act
Although Heiji is close to solving the case, he pretends not to understand the answer. That leaves Conan with a problem. If Heiji explained the solution, Conan could stay in the background. With Heiji apparently unable to do so, Conan has to find another way to deliver it.
Conan chooses his familiar technique: the Stun-Gun Wristwatch puts Heiji to sleep, and the Voice-Changing Bowtie lets him give the deduction in Heiji’s voice. Heiji’s test has drawn out the method behind Conan’s deception.
This is what makes Heiji’s role satisfying. He is not waiting for the secret to fall into his lap. He creates a situation, watches the response, and checks whether it fits his theory.
He wakes during the deduction and keeps pretending to sleep
Heiji regains consciousness before Conan finishes. Instead of immediately getting up, he remains still and sees Conan speaking in his voice. The unusually sharp child now has a concrete means of presenting an adult detective’s reasoning without taking the credit.
“You’re Kudo, aren’t you?” (unofficial translation)
Heiji confronts Conan with the identity he has worked out. Conan can no longer dismiss the question after being caught in the middle of the performance.
The reversal is the heart of the scene. The watch and bowtie have repeatedly helped Conan hide. Here, using them on a detective who is already suspicious gives that detective the evidence he needs.
Why Heiji did not know at their first meeting
Heiji first appears in the diplomat case, in Japanese episodes 48–49 and Volume 10. He visits the Mouri Detective Agency because he wants to test Shinichi’s ability. At this point, he treats Conan and Shinichi as separate people.
He gives Conan Chinese liquor, after which Conan temporarily returns to Shinichi’s body. Heiji then meets Shinichi at the crime scene and has a mistake in his deduction pointed out. His attention is on the rival standing in front of him, not on connecting that rival with Conan.
That encounter still matters to the later discovery. Heiji has seen Shinichi’s judgment firsthand and can compare it with Conan’s behavior. He has also seen Shinichi place the truth above winning a contest, changing the nature of his interest in him.
The two cases therefore form a progression: first Heiji gets to know Shinichi as a detective; then he notices that Conan thinks in a disturbingly similar way. The gadgets provide the decisive evidence, while their first meeting gives the suspicion its context.
Knowing Conan’s identity does not mean knowing every secret
Heiji knows that Conan Edogawa is Shinichi Kudo, living in a child’s body and concealing his identity. His later behavior depends on that knowledge: he calls him “Kudo,” cooperates in investigations, and helps maintain the disguise.
The reveal does not establish that Conan immediately briefs him on every detail of APTX 4869 or the Black Organization. Later cooperation is also not proof that Heiji has received a complete account of every member, operation, and discovery.
Conan often limits what he shares to avoid drawing others into danger. It is reasonable to think that Heiji receives information as it becomes necessary, but the story does not give a fixed, comprehensive boundary for his knowledge. “He knows Conan is Shinichi” is the firm answer; “he knows everything Conan knows” goes further than the evidence.
Heiji does not deliberately tell Ran or Kazuha the truth. Ran’s own suspicions are a separate matter, and Kazuha’s closeness to Heiji does not establish that she shares the secret.
The discovery turns a rival into a partner
For Conan, being found out usually means danger. With Heiji, it also creates a rare opportunity: he can exchange deductions with another detective his own age without maintaining the fiction that he is an ordinary child.
Heiji brings his own reasoning and can act openly as a high school detective where Shinichi cannot safely appear. Their partnership is more than Conan giving instructions to someone who speaks for him; they can challenge and support each other’s conclusions.
Calling Conan “Kudo” captures both sides of that closeness. In private it acknowledges the person Heiji knows. In front of Ran, Kazuha, or others, the same familiarity risks exposing him. The comedy works because the secret underneath it still has consequences.
The reveal in episode 58 and File 121 is memorable for that change in direction. Heiji’s investigation threatens Conan’s disguise, yet the person who sees through it becomes someone willing to protect it.
Revisiting the earlier diplomat case before this one makes Heiji’s changing view of Shinichi easier to see. What begins as competition becomes one of Conan’s most important equal-footed detective partnerships. For another identity reveal, see when Shuichi Akai learns Conan’s secret.
Further reading (contains spoilers): Heiji and Kazuha's relationship timeline and when Kaito Kid learned Conan's identity.
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