Jean-Jacques operates under the assassin alias "Tarantula." His path crosses the main narrative involving Randy Cortot and Jeudi/Alicia Brendel. A key revelation later exposes Jean-Jacques as Randy's brother. This discovery unfolds amidst the larger conflict driven by Count George de Germont's ambitions. Jean-Jacques's actions intersect with the protagonists' journey as they confront the Count and pursue Jeudi's past.

Set against the turbulent backdrop of early 20th-century Europe and rising Nazi influence, where Count de Germont seeks power, Jean-Jacques's profession as an assassin ties into the era's political and social tensions. His familial bond with Randy introduces personal stakes into the overarching conflict, positioning him to impact the protagonists' efforts.