Bret Vyon's turn to increasingly desperate and immoral actions in his effort to warn Earth.

The Doctor leaves the TARDIS unguarded after instructing Katarina to secure it, his impulsive departure creating a critical vulnerability. Bret Vyon, who had been hiding nearby, seizes the opportunity—first examining …

Katarina, following Bret’s insistence, administers mysterious tablets to the feverish Steven in an attempt to stabilize his blood poisoning. The moment of fragile trust is shattered when Bret, mid-instruction, spots …