Dr. Stone Wiki
Dr. Stone Wiki

Fire the Smoke Signal (狼煙をあげろ Noroshi o Agero) is the fourth episode of the Dr. Stone anime. 


Senku, Taiju, and Yuzuriha arrive at Mt. Hakone in search of weapons of science. In order to fight against Tsukasa, they use sulfur to create gunpowder. The group accidentally causes an explosion, creating a smoke signal. This signal is returned, indicating nearby humans.

Tsukasa arrives, having seen the signal, and takes Yuzuriha hostage. Senku provides Tsukasa with the Revival Fluid to set her free, but refuses to revoke science when demanded, recalling his life as a child learning about science. Tsukasa decides to kill Senku, perceiving him as a threat to his goals.

Plot Details[]

Sitting in the hot springs, from which a fence separates them, Yuzuriha asks Taiju what he was going to say on that day 3,700 years ago. Taiju replies that he couldn't live with himself if he revealed it now in Stone World. He asks Yuzuriha to wait until they have rebuilt civilization, and she agrees that they will save humanity.

Senku gathers gunpowder ingredients

Senku gathers the ingredients for gunpowder.

The next day, Senku gathers the three materials needed to make gunpowder, and now all they need to do is mix them. Ingredient one is sulfur, which is plentiful at the hot spring. The second ingredient is charcoal, which burning wood can easily make. The last and most difficult ingredient is potassium nitrate, but Senku made some ahead of time. Taiju recognizes nitrate from the miracle fluid they make. To make viable gunpowder, they need to mix the ingredients with a pinch of sugar.

Taiju prepares to pound the mixture with a large rock to finish the process, but Yuzuriha is concerned it may cause an explosion. Senku reassures her that stone on stone won't cause an explosion, but flint and stone will, only to remind himself of the iron present in the pyrite boulder Taiju is using. Everyone moves in time to avoid the detonation, and Senku calls this test a resounding success.

Senku vs

Senku vs. Tsukasa!

Yuzuriha asks if they plan on using gunpowder to fight Tsukasa, but Senku replies that he plans to bargain with him. Senku plans to kill Tsukasa if negotiations fall through, and Tsukasa plans to kill the former if he's already made gunpowder. Senku laments having revealed their location due to the smoke from the explosion. However, Yuzuriha points out a responding smoke signal in the distance, which other humans have undoubtedly lit.

Senku is faced with the choice of putting out the fire to conceal their location or lighting it to reveal themselves to potential allies. The young scientist goes with his gut and chooses the future by lighting the smoke signal again.

Tsukasa rushes through the forest, chasing after Senku's trail. He knows Senku withheld the fourth usage of seashell powder as a safety precaution. He eventually stumbles upon the smoke signal and finds Yuzuriha soon after. Tsukasa takes the girl hostage and confronts Senku, demanding he stop tainting the world by reviving weapons of science.

Young Senku experimenting

Senku's passion for science began at an early age.

Senku taunts him for being so gracious about this death sentence, but Tsukasa says he needs to know the recipe for the miracle fluid first. Senku tries to bluff as if he doesn't care for the girl, but Tsukasa abruptly cuts her hair and tells him to stop stalling. Tsukasa called his bluff because he knows the most logical thing would've been to bury Yuzuriha while she was petrified. He claims victory because Senku has people he holds dear, while Tsukasa thinks no human is precious.

Yuzuriha suddenly points Tsukasa's blade at herself and begs Senku not to reveal the recipe. Rather than allowing the girl to come to harm, Senku reluctantly reveals the recipe for the miracle fluid. Tsukasa no longer has a reason to keep Senku alive but promises to spare him if he sacrifices science for the rest of his life.

Tsukasa admits Senku could have been a friend

"You may have been my first friend."

Senku recalls learning about science and how it connected him to his best friends from childhood, Taiju and Yuzuriha. With those memories weighing on his heart, Senku replies that giving up science is the one thing he could never do. Disappointed, Tsukasa promises to give Senku a merciful death and even says they could've been friends if not for the circumstances. Taiju returns to the scene too late and sees his best friend slain.







  • Mount Hakone


  • Gunpowder

Anime to Manga Differences[]

  • There's no recap on what happened so far in the anime.
  • There's an additional scene in the anime where Taiju becomes a cameraman.
  • A panel showing a bombed Tsukasa in Yuzuriha's imagination is omitted from the anime.
  • The further explanation of the Senku-Tsukasa deal is omitted in the anime.
  • The side story included in Chapter 9 is omitted in the anime.



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