Pavo was pursuing the Monk and caught up with him at a research station. However, the Monk shot him with Pavo's own baton. The Monk then stole Pavo's perception-altering ring in order to impersonate him.
The Monk thought that he had killed Pavo, but with the help of the Second Doctor and Jamie McCrimmon, he was able to regenerate. Pavo's new incarnation was a woman and assumed the alias of "Commander Melanie Flail".
Pavo intended to also arrest the Doctor, but eventually, after the Doctor helped her defeat the Monk and a Seeth invasion, she decided to let him go this time, after hypnotically wiping the Doctor, Jamie, and Victoria's memories of the event, "officially" claiming that this would help her escape the taint of requiring the aid of a renegade to resolve this crisis. (AUDIO: The Black Hole)
Behind the scenes
Although not explicitly stated in the story, Simon Guerrier intended for the two Pavos to be earlier incarnations of the Master. "Pavo", Latin for "peacock", was chosen to fit the Master's personality. Hints towards this identity in the story include the "curious silver baton" wielded by Pavo as a weapon, as well as the hypnotic abilities she displayed. The Master had earlier been suggested in the novella Time and Relative to have originally been an agent of Time Lord law enforcement tasked with tracking down Renegades, much as Pavo does in The Black Hole.