Magister Cassian Wyrm is lean enough that his high-collared coat seems to hang from a rack of narrow bones. His white scales have the matte, faintly pebbled finish of old ivory, with a dusting of gray along the jaw and throat. He moves in economical, gliding steps, but pauses abruptly whenever someone meets his gaze, turning his head as if tracking a sound behind them. His broad dragonborn jaw and blunt, interlocking teeth show whenever he chews; he eats dried fish in small, methodical bites, never looking up. A tiny wooden wind-up beetle is tucked in his coat pocket, its polished shell worn bare on one side from his thumb. It is an unexpectedly childish keepsake on a scholar who insists that sentiment is a poor filing system.

Cassian is exacting and guarded, yet unexpectedly patient with frightened novices. He distrusts sentiment in public and is secretly sentimental about small, useless objects. Under pressure, he becomes brisk and controlling; in private, after a safe meal or a good discovery, dry humor slips through and he can talk for hours.

Cassian was raised in the river-port district of Vellum Quay, where his mother copied shipping manifests and his father repaired winter stores. As a boy, Cassian learned to read by tracing numbers on crates, then discovered that old books could explain why the river froze in patterns no local almanac predicted. He won a scholarship to the Collegium of Measure and became a meticulous scholar of weather magic and dragon migration. His life changed during the White Thaw, when a spell meant to redirect a lethal flood instead trapped a neighborhood under a sudden sheet of ice. Cassian survived by breaking a ward he had sworn to preserve; his younger sister, Sella, saved trapped residents and lost the use of two fingers to frostbite. He has spent years documenting the disaster honestly, though the Collegium quietly blamed a dead assistant. Sella now runs a ferry repair shop and refuses his money, while his former mentor, Ivar, presses him to publish a sanitized account. Cassian is currently searching for the original ward-stone, which may prove the flood was no accident.