In a recent sale, I picked up a two-disc Companion Chronicle called "Peri and the Piscon Paradox." It's one of the rare CCs that has an actual Doctor providing the second character's voice.
This is a two-disc set, starting with a very early Peri and Fifth Doctor, and also stars Colin Baker as the Sixth Doctor.
It starts out light and fluffy and just plain funny, then takes a turn. Nicola Bryant shows more range with Peri in this story than she showed through all of her on-screen appearances combined.
And for good measure, we also find out the answer to a question that has been hanging out there since Trial of a Time-Lord aired. I finished listening to it last night, and am still thinking about it.
There ... Praising it without spoiling it. The less you know going in, the more impact it has.