Captain Black returns for this episode, once again as a bad guy.

And the Sonic Rifle is the Mysteron Gun from Spectrum Strikes Back.

This episode's scenes with Matthew and Rex are my favorite moments in the entire series.

I do wish that they had shown Matthew reacting more to Rex's overtures. Or perhaps Father Unwin asking why he smelled so "doggy".

Agent Blake has been carefully kept in the dark about Father Unwin. In this episode, they show him standing in Bishop's office while Bishop speaks with Father Unwin. Bishop refers to Father Unwin's "parishioners". Unless Blake is really slow on the uptake, which doesn't seem likely considering the work he's in, Blake now knows that Bishop has a clergyman in the spy business.

The bad guys are definitely slow on the uptake. Never noticed that Father Unwin came in with a briefcase, but came out emptyhanded!

Perhaps the Professor was working on the sonic rifle in order to make enough money to renovate his home. The room where they were keeping his daughter looked a real mess.