Serge confronts armed loyalists with pistols and the old no-guns rule, then dies from a rifle shot before he understands they have abandoned restraint.
Serge preserves a hidden communications back door after Ashford's supporters seize official systems, then organizes trusted Behemoth security into small squads. He knows the ship better than the mutineers, estimates their strength, and intends to clear loyalist wolf packs from the drum while Bull hides. His confidence rests on the assumption that fellow crew members can still be contained through policing.
Near the refugee tents, Serge rounds a corner with six pistol-armed officers, including Corin, and faces at least twelve Belters holding assault rifles and shotguns. He invokes the standing rule against guns in the drum and identifies his group as the police when a woman points out their sidearms. She answers that they are not police anymore and shoots him through the forehead. Serge sinks with puzzled surprise as the loyalists disarm and bind the survivors. His death marks the moment the counter-mutiny ceases to be a contest of shipboard authority and becomes an armed regime willing to execute colleagues without warning.
Serge is an adult Belter man with a split-circle tattoo on his neck, stubble, and a rumpled security uniform. At death he wears a faint confident smile and keeps one hand near his holstered pistol.
Serge is the loyal security deputy whose summary execution reveals that familiar procedures and collegial restraint no longer govern the Behemoth.