Necessary Evil

A beautiful Bajoran woman, Pallra, calls Quark to Bajor and persuades him to retrieve a strongbox her late husband kept hidden on Deep Space Nine. He agrees, unaware that a stranger named Trazko has observed their entire interaction, with Pallra's knowledge. Later that night, Quark and Rom sneak around the Promenade until they find the hidden panel that conceals the strongbox. Quark opens the box and sees that it only contains a list of Bajoran names. Suddenly, Trazko appears, and Quark realizes that Pallra probably sent him. Trazko takes the list from Quark and shoots him with a phaser, apparently killing him and leaving a panic-stricken Rom shouting for help.

While Bashir works frantically to save Quark, Odo questions Rom about the robbery and attack. Rom denies knowing what Trazko took from Quark, but when Odo accuses him of killing his brother, he tells him about the list. When Rom tells Odo the box was found on the site where the station's old chemist's shop used to be, Odo flashes back to a conversation he had with Gul Dukat five years earlier. The owner of the shop, Vaatrick, was murdered, and Dukat essentially forced Odo to investigate the killing. Odo questioned the dead man's widow, Pallra, about her husband's death, but while he was suspicious of her, she said her husband's alleged mistress probably killed him in a jealous rage. That mistress, she said, was Kira Nerys. Odo then comes out of the flashback and realizes that the attack on Quark could be related to this still-unsolved murder.

Odo tries to help Rom remember the names on the list. Rom can only remember one, which he thinks is Ches'so, and Odo then asks Kira if she knows the name. Kira says she does not, and Odo has another flashback to the time he interrogated Kira about Vaatrick. Kira denied the murder and the alleged affair, saying only that she and Vaatrick were friends. Later, Odo became even more suspicious when he spotted Dukat and Pallra kissing. This feeling remains after his flashback ends, sending Odo to Bajor to question Pallra about the list of names. She denies knowing anything about it, and says she does not recognize the name Ches'so. Odo then asks her how she found the money to pay her power bill, telling her that he knows her power had been cut off for non-payment. Pallra says a friend gave her the money but refuses to identify him.

While Quark continues to fight for his life, Kira tells Odo that she located Ches'so, whose real name is Ches'sarro, but that he drowned mysteriously the previous evening. Sure that Pallra is somehow involved, Odo orders a full examination of the man's death as well as an investigation into Pallra's bank records. Odo then has another flashback to when he first met Quark, remembering that Quark told Odo that Kira paid him to say she was at the bar the night Vaatrick was murdered. Sometime after the flashback ends, Odo shows Sisko the list of Bajoran names, which he compiled after looking through Pallra's communication records. Since every man on the list apparently transferred Bajoran currency into her account, Odo realizes that Pallra has been blackmailing them by threatening to expose their collaboration with the Cardassians.

Odo then flashes back to a conversation he had with Kira in which he confronted her about paying Quark to be her alibi. Kira once again insisted that she did not kill Vaatrick, but admitted that she was a member of the Bajoran underground and had sabotaged the ore processor the night he was killed. Since the crime was punishable by death, Odo mentioned nothing of it when Dukat entered the room, and simply told the Cardassian that Kira was not their murderer. Back in the present, Trazko enters the Infirmary with plans to finish Quark off, but Rom appears and the two begin fighting. The melee is loud enough to attract security, and Odo arrives to take Trazko to a holding cell. Later, Odo arrests Pallra for blackmail, despite the realization that Kira did kill Vaatrick that night five years ago — not because they had an affair, but because he was a Cardassian collaborator who caught her trying to steal the list. While he has no intention of prosecuting her and — says they can remain friends, both Odo and Kira realize the bond of trust between them may be changed forever.