'Who kills by iron')[n. 1] is a 2019 drama-thriller film directed by Paco Plaza, written by Juan Galiñanes and Jorge Guerricaechevarría and starring Luis Tosar, Xan Cejudo, Ismael Martínez, Enric Auquer and María Vázquez.

In prison, semi-retired drug lord Antonio Padín (Xan Cejudo) is given a series of tests, showing that his mobility is limited, and decreasing due to an unnamed condition.

Padín is released from prison due to his medical state, and picked up by one of his children, Toño (Ismael Martínez) who says he is here to take him home.

Cut to Mario (Luis Tosar) and Julia (María Vázquez) at a class for pregnant couples.

After the class ends she drops him at his work; he is head nurse at an assisted living facility.

Another staff member, Ana (María Luisa Mayol) informs Mario that Padín will be coming to stay there.

Mario runs Padín through some simple hand stretches to improve his mobility, seeming to earn a begrudging trust from the older man.

Back at home a news report about Padín affects him strongly but he hides this from Julia, his wife.

He is shown preparing the drugs (heroin) at the hospital, drawing it into a syringe that he injects between Padín's toes after telling the man it's not oral medication so it won't "tax his throat".

They visit the nursing home where they see Padín with a group of other seniors, playing a game with a parachute.

While listening to the heartbeat, Mario has a flashback to a younger version of himself injecting something into an unknown person's arm in what appears to be a drug den.

Toño is shown nervously waiting by several cell phones in an office at a packing plant.

Kike calls him twice before pulling out a different phone and having a coded conversation about rice with a truck driver.

Kike's car is shown to have a tracker on it, which leads the police directly to the packing plant where Toño was.

Mario informs them that he feels Padín's physical condition is worsening quickly and other staff agree.

Toño is shown talking to his lawyer who assures him the evidence is all circumstantial, and all they need to do is bail Kike out.

Toño admits that Padín refused to help leading Kike to break down and cry from fear.

Xepas (Dani Currás) arrives in a camo truck and motions for him to get in before taking him to meet Toño.

Xepas roughs him up before letting him out of the truck and informing Toño that he recognized Mario from years before; he used to buy "horse" (heroin) from the bar.

Mario retrieves the syringe he killed Padín with and cleans his fingerprints off before pressing it to Toño's hand.

The film was produced by Vaca Films, Atresmedia Cine and Quien a hierro mata AIE alongside Playtime Production and it had the participation of Atresmedia, Movistar+, TVG and Netflix and support from ICAA, AGADIC [gl] and Creative Europe's MEDIA.