Vandercaust's wary eye finds the single false malfunction that turns Medina's apparent victory into a warning of an attack on the alien station's rail guns.
Vandercaust is the oldest member of a Medina technical workgroup with Salis, Roberts, and Jakulski. Free Navy security has already beaten and interrogated him over an earlier attack, leaving him guarded and acutely aware that the government can turn ordinary associations into guilt. The prospect of another battle sends him to the public feed with his coworkers rather than into political argument.
During the assault, Vandercaust joins the others in watching the rail guns and PDCs shred the incoming swarm. He points out that the weapons force attackers to rush and accepts that Medina has been bruised but not immediately taken. Unlike the bar's celebrants, however, he cannot explain why some craft drift out of the safe shadow where they might have threatened the station and make themselves easy rail-gun targets.
Tracking one presumed malfunction on his hand terminal, he sees its dead drift become deliberate motion toward the central blue Ring Station. His analysis supplies Roberts with the proof that the massive swarm was a magician's gesture: the real operation is aimed at the rail guns beyond Medina, where the station's defenders have been distracted from looking.
An older, weathered Belter technician with a bruised cheek, swollen eye, tired wary eyes, and a split-circle OPA tattoo on his wrist; he wears rumpled work clothes and works a hand terminal with thick fingers.
Vandercaust turns survivor's suspicion into the observation that detects the assault's hidden line of attack.