The Companion Chronicles is a series currently produced by Big Finish Productions. The plays are mainly tales recounted by one of the Doctor's companions with another actor featured in a supporting role.
Originally, the concept was to produce talking books featuring the companions of the doctors who are unavailable to take part in the main audio range (due either to death or refusal). However, the range is now expanding featuring characters who are not strictly companions and companions of doctors who are featured in the main range.
Some plays tie in to other plays in the Big Finish Doctor Who range. The Darkening Eye is a prequel to The Death Collectors, and in The Prisoner's Dilemma, Ace meets Zara, Amy's sister and a fellow tracer.
The plays also reveal what has happened to the some of the companions since they left the Doctor. For example, it is revealed that Vicki remained with Troilus and had a large family, but she never felt like she fitted in. Leela survived the Last Great Time War, but lost the anti-aging protection that the Time Lords gave her. Susan stayed with David Campbell, and Victoria settled down and raised a family.