Episode 4 of "Bloody Flower" commences with Han-jun attempting to persuade the judge, who remains unyielding in her verdict. Rather than celebrating their victory, Prosecutor Cha promptly heads to the crime scene of the strangled man, identified as Hong Min-su, a doctor at Cheum Medical Centre where Woo-gyeom and Professor Han were employed. Dr. Hong was instrumental in approving Woo-gyeom's clinical trial and subsequently left the hospital to co-found Jinnam Research Institute alongside Professor Han.
Returning to Woo-gyeom's case, he has appealed the death sentence but faces a new judge, Choi, who is a close friend of Director Oh (Prosecutor Cha's superior). Han-jun realizes that they require a contingency plan as Choi is highly likely to reject the medical demonstration. In the meantime, Prosecutor Cha visits the Jinnam Research Institute, where a man flees upon seeing her. She loses sight of him but captures him on CCTV.
Woo-gyeom is moved from isolation to a shared cell, where one of his cellmates is the brother of Hong Jae-gwang, the last victim. As anticipated, the inmates launch an attack on Woo-gyeom during the night. In the ensuing chaos, Inmate Bae Geun-hyeok is stabbed in the leg. Woo-gyeom takes the upper hand and pretends to attack until the guards arrive. He then feigns a seizure, and once rushed to the hospital, he requests Professor Han's presence.
A flashback reveals that this was all part of a planned unofficial demonstration orchestrated by Han-jun. They select Inmate Bae due to his Congenital Corneal Damage. We witness Woo-gyeom devise the actual plan. While Han-jun expresses concerns about the risks, Woo-gyeom is unconcerned about the appeal, solely focused on proving his skill.
Currently, Woo-gyeom administers a blood transfusion to Inmate Bae, which heals the latter's stab wound and corneal damage. Professor Han verifies that Woo-gyeom's blood in Bae is the cure. An overwhelming majority of the public demands a demonstration, and Han-jun threatens to file a constitutional petition. Under this pressure, the court agrees to the demonstration, overseen by Cheum.
Elsewhere, Prosecutor Cha witnesses Professor Han's visit to Woo-gyeom in prison. Before she can delve deeper into his background, Chief Pyo, the chief of staff for Assemblyman Baek, arrives. He shares intel that Min-seo is battling Batten disease and is one of the applicants for the demo. Additionally, Han had conducted experiments on Woo-gyeom while he was in a coma. Chief Pyo refuses to reveal his source, asserts that the mess has been taken care of, and warns Prosecutor Cha not to dig too deeply.
Following Pyo's ominous warning, Professor Han vanishes from sight. Han-jun is bewildered by these developments, but Woo-gyeom doesn't seem to care. There seems to be no love lost between mentor and mentee. Woo-gyeom claims that Professor Han failed to create the cure himself and is bitter that Woo-gyeom succeeded. He visited him in prison for answers but received nothing in return.
That night, Prosecutor Cha visits Han-jun. She is emotional, as he was her role model and she used to look up to him. She wishes he had told her about Min-seo and promises to help. In response, Han-jun confesses that he hates himself for defending Woo-gyeom but sees this as his last chance.
All this drama comes to naught as Choi Woo-jin, a young boy with cancer, is selected for the demo. Following the blood transfusion, the court allows a 24-hour wait period.
In the meantime, Detective Gong identifies the Jinnam runner, Shin Ho-chang. He has an interesting criminal record involving fraud and murder for which he was just suspended. And the prosecutor was Director Oh Hyeon-deuk! There was also a medical violation involving Professor Han over which Director Oh presided and dismissed. Prosecutor Cha is shocked and wonders if Director Oh is involved in the clean-up that Chief Pyo mentioned.
Not even a few hours later, Woo-jin wakes up, fully recovered. At the end of the episode, Chae Jeong-su, the chairman of Cheum Medical Center visits Han-jun.
