"Haroche had avoided facing his victims, Miles had noticed. He'd never once visited Illyan in ImpSec's own clinic, had tried unsuccessfully to avoid Miles back when he'd doubtless been planning the original version of the frame-up, and had been careful to enter the Imperial Residence only after Galeni had been arrested and removed. He was not, perhaps, an evil man, but only an ordinary smart man tempted to one evil act, and then overwhelmed when its consequences proliferated beyond control."
―Caught in the act of concealing his crime.[src]

Lucas Haroche was a general in Barrayaran Imperial Security, and Head of Domestic Affairs. He began his military career as an enlisted man in Service Security, and was a military policeman and non-commissioned officer before receiving his commission. While he was a Domestic Affairs agent he foiled four plots against Gregor Vorbarra's life, as well as the Yarrow plot to destroy the Imperial Residence.

He became Head of Domestic Affairs after the Yarrow incident. After the temporary death of Miles Vorkosigan, he became Simon Illyan's second in command. Less than a year later, however, Illyan approached him and asked him to train Vorkosigan as his assistant, in preparation for taking over the role of Chief of Imperial Security.

Vorkosigan was fired shortly thereafter, and Haroche remained Illyan's second in command. He was ambitious for more authority, however, and sabotaged Illyan's memory chip with a Komarran bioweapon, framing Vorkosigan for the crime. He became provisional Chief of Imperial Security, and used his powers to stymie any investigation into Illyan's condition.

However, Vorkosigan was appointed an Imperial Auditor to oversee Illyan's case. In investigating the chip breakdown, he was able to determine the cause of the failure. After the frame on Vorkosigan collapsed, Haroche framed Captain Duv Galeni and had him arrested. Like Haroche himself, Galeni had an induced fast-penta allergy, and so was unable to clear his own name. Haroche then attempted to bribe Vorkosigan to drop the case, but betrayed himself as the culprit in the process. He was arrested for treason, but decided to confess and cooperate in the hope of facing a lesser charge.