WARNING: The following article contains spoilers for Season 1, Episode 4 of Dr. Stone, "Fire the Smoke Signal," now streaming.
Dr. Stone's fourth episode is an explosive one in both a metaphorical and very literal sense. While Senku and Tsukasa's civil war reaches a fever pitch, the episode also features actual gunpowder.
Tsukasa and Senku came to blows not long after the "primate" high-schooler was revived in the Stone World. While Senku plans on extending his stone-breaking formula to all of humanity, Tsukasa favors a much more selective process. His method involves destroying the bodies of the world's older population while they're still encased in stone, something he describes as a "cull," but Senku defines as plain murder.
The scientist quickly realizes that stronger weapons than a second Stone Age can provide are needed to put a stop to the unusually powerful teenager, so he takes Taiju and the newly revived, Yuzuriha on a hiking trip in search of a new material: sulfur, a foundational ingredient in gunpowder.
They successfully engineer the substance but, in doing so, set off a smoke signal that quite plainly gives their position away. To their amazement, another plume of smoke appears in the near distance. Is it Tsukasa, waving the white flag? No, this is the first sign of another, walking and talking person in the Stone World: a young woman with blonde hair, as a brief glimpse of her reveals. Senku finds himself, once again, torn between his immediate and long-term survival. The smoke being thrown up into the air will undoubtedly attract Tsukasa to their location unless extinguished. On the other hand, it may also attract a new potential ally. Riskily, he decides on the latter.
We hardly have any time to dwell on this new development, however, since Tsukasa predictably arrives at their temporary camp. He wastes little time in taking control of the situation, holding Yuzuriha hostage and demanding that Senku gives him his Stone Formula in exchange for her life and stops using it to revive people. Senku's protests that he doesn't care for the girl fall on deaf ears, as does Yuzuriha's insistence that her life pails into comparison against the rest of the human race.
Reluctantly, Senku gives up his recipe to save Yuzuriha's life, only to find his own in jeopardy. Proving (badly) that's not a total monster, Tsukasa gives the genius another ultimatum. If he denounces science, he gets to keep his life. As Senku considers the offer, warm memories of a childhood spent conducting weird experiments and dreaming of space exploration come flooding back to him -- memories that include the way his odd pursuits formed the ties of friendship that have endured thousands of years into the future. His answer, of course, is a "no" to Tsukasa.
True to his word, a wistful Tsukasa promises a quick and painless end before delivering what appears to be a killing blow, just as an absent Taiju comes rushing onto the scene, leaving the episode on a dramatic cliffhanger.
New episodes of Dr. Stone air every Saturday night as part of Cartoon Network's Toonami block, and on Crunchyroll.