A Section 31 operation of 2375 in which Julian Bashir was unknowingly used at a conference on Romulus to protect a Starfleet informant, the Tal Shiar chairman Koval, and ruin Senator Cretak.
The Koval affair is the plot of the Deep Space Nine episode Inter Arma Enim Silent Leges. Sloan of Section 31 asks Bashir to attend a medical conference on Romulus and observe Koval, head of the Tal Shiar, who is thought to be ill and is expected to join the powerful Continuing Committee. Bashir comes to believe that Sloan intends to kill him.
Getting no help from Admiral William Ross, Bashir warns Senator Cretak, an ally of the Federation, and she tries to obtain Koval's files. Both are arrested. At the hearing Sloan is revealed, seems to be shot while fleeing, and Cretak is condemned for treason.
Bashir works out the truth on the journey home. Koval has long been passing information to Starfleet, Cretak was his rival for the committee seat, and the whole episode was arranged to remove her. Ross admits that he took part.