Sean Ambrose, a disavowed IMF agent and Ethan Hunt’s former "double," steals Bellerophon after murdering Dr. Nekhorvich.
The "deep story" is built around two biological agents named after Greek myths:
During a raid to destroy the virus, Nyah injects herself with the last remaining sample of Chimera to prevent Ambrose from obtaining it.
The only known antidote, which must be administered before the 20-hour window closes.
In Greek mythology, the hero Bellerophon defeated the monstrous Chimera. Dr. Nekhorvich, the virus's creator, purposefully gave them these names to reflect the "hero" (cure) and "villain" (disease). Key Story Beats
Ethan must fight his way through Ambrose’s stronghold to retrieve the Bellerophon antidote before Nyah dies. Chimera - Mission Impossible | Fandom