Ambassador Londo Mollari (Peter Jurasik) is contacted by a Centauri senator (Damian London). The Emperor and the Centaurum believe he must try harder to improve relations with other races. Afterwards, he leaves his quarters and runs into Lennier (Bill Mumy). He asks Lennier about Ambassador Delenn (Mira Furlan), who is away, and they talk. When Lennier says he only knows other races from what he reads about them, Londo invites him to hang around for a day and get some real information. In the Babylon Five courtroom, Ombuds Wellington (Jim Norton) finds Karl Mueller (creepy actor Mark Rolston) guilty of murder, to be sentenced the next day.

Ivanova (Claudia Christian) visits a free clinic in the Downbelow, established by Doctor Franklin (Richard Biggs) without official authorization. She is miffed not to have been informed but will not shut it down. Wellington discusses Mueller’s sentencing with Commander Sinclair (Michael O’Hare), Chief Garibaldi (Jerry Doyle), and telepath Talia Winters (Andrea Thompson). Garibaldi wants him spaced, sure that he has killed more than they think, but that is not legal. A mindwipe is possible, though Talia has had unfortunate experiences in the minds of killers.

Down below, Franklin meets a faith healer named Laura Rosen (June Lockhart) who has an alien healing machine. Her daughter Janice Rosen (Kate McNeil) defends her mother’s work, though Franklin thinks she is a con artist. Mueller, sentenced to mindwipe, has to be dragged from the courtroom. Franklin is still not sure about the ethics but agrees to set up the procedure. He asks Garibaldi to check out Doctor Rosen. Londo brings Lennier to the Dark Star Club. Lennier wants to bail at first because of the dancing girls, but Londo needs him to pay for the drinks. Lennier avoids alcohol by telling Londo that it makes Minbari homicidal.

Franklin learns that Rosen was a real doctor until her addiction to stims. She lost her license when a patient died. But she found a way to heal people. Franklin’s continuing questions irritate her daughter. Lennier’s boring stories about learning 97 Minbari dialects irritates Londo until he learns about Lennier’s talent for probability mathematics. He invites Lennier to learn an Earth game called Poker. Talia steels herself to perform the mindwipe, but first Mueller has to be scanned. She is horrified to discover his many murders. Franklin studies the health records of Rosen’s sessions with the alien healing device, and the remarkable results. The subtler points of Poker are beyond Lennier, but he wins a lot.

Franklin attends a session at Rosen’s clinic. The alien device transfers life energy from one person to another, which is slowly killing her, but she is dying of Lake’s Syndrome anyway and doesn’t want her daughter to know. Franklin agrees to keep mum if he can treat her and see her patients’ records. Garibaldi finds Talia in the station’s gardens and she tells him Mueller is a mass murderer. At the poker table, a tentacle comes from below Londo’s vest and steals cards. Mueller takes off during his last walk, and Garibaldi shoots him, but he is only wounded, steals a gun, and disappears into the Downbelow.

Londo is caught cheating. A player attacks him, but Lennier defends him, only to be surrounded by angry players. Franklin finds Mueller in the free clinic holding Rosen and her daughter at gunpoint. Mueller is forcing her to heal him, which is killing her. But when he is distracted by Franklin, she reverses the machine. Her Lake’s Syndrome is cured, and Mueller dies of it, screaming in pain. The next day, Ombuds Wellington finds her not guilty by reason of self-defense, though he takes the dangerous machine into Babylon custody. Ivanova finds Garibaldi and identifies the two aliens involved in the bar-fight in Dark Star—Londo and Lennier.

Sinclair meets with them. Lennier takes the blame, saying that he misunderstood how poker is played. They both have diplomatic immunity anyway, and the charges are dropped, providing the damages are paid for. Afterwards, Lennier explains to Londo that the Minbari believe it is honorable to lie to help others save face. Lennier asks about the tentacle and is told about the unusual Centauri genitalia. Lennier makes a hasty retreat. Doctor Rosen turns over the alien machine to Franklin.

June Lockhart and Bill Mumy did not appear together in this story, and were not even filmed on the same day, though they did appear together every week on Lost in Space. Straczynski was tempted to have them meet but realized that people would talk about nothing else. He wrote this story suffering from the flu and bronchitis with no memory of doing so. He awoke one morning and found the script on the table. Lennier’s fighting technique is that of Caine (David Carradine) in the series Kung Fu. The Dark Star was named after the cult SF movie by John Carpenter. The Ombudsman was created by Harlan Ellison, who was a consultant on the series and wrote several episodes. Presumably, he found working with Babylon Five more congenial than his documented conflicts with Star Trek.

Throwing people out of airlocks is used only for mutiny and treason. Garibaldi comes by his Dirty Harry sense of justice honestly, as Jerry Boyle was the son of a Brooklyn cop and became a right-libertarian radio host. He was also a stockbroker and a jet-pilot. His first acting role was on the series Moonlighting, where he played the doppelganger of his lookalike Bruce Willis. He died in 2016. He was married to Andrea Thompson (Talia Winters). A telepathic scan is inadmissible in court because it lacks due process. Few telepaths can handle criminal cases without burnout. The station lockup is overcrowded and there is no room for life-sentences. The poor in Downbelow have to pay for medical treatment and most cannot.

Centauri males have six prehensile penises, and Centauri females have six slots in their lower back. They do not produce litters of six, however. Two women in the prop department kept bringing Londo’s tentacle to Straczynski for verification. He thought they were having way too much fun with it. June Lockhart was great in the episode; Bill Mumy and Peter Jurasik are always great and make a wonderful Laurel and Hardy team. Just as the episode Believers has been called anti-religion, pro-religion, and religion neutral, The Quality of Mercy has been called both pro and anti-capital punishment—no doubt exactly what Joseph Michael Straczynski wanted. The alien healing-device will show up again later.