Big Finish Doctor Who/Recap/S1/E05 Phobos/NEDA

The Doctor parks the TARDIS on a cliff (again). They're on Phobos, Mars' moon, which suddenly has an atmosphere and lots of opportunities for extreme sports. The Doctor thinks that's kind of unusual, especially since there's a mad scientist, Kai Tobias, going around babbling about monsters.

A human woman named Amy and her alien lover Farl are on the run and pretend to be on holiday. It turns out that Farl's species wants to keep the bloodline pure, and don't take kindly to Amy. Their own violent Fantastic Racism causes a lot of backlash, and Farl faces discrimination everywhere he goes.

Kai turns out to be right: there is a monster, and people are dying. The local "Drennies" (adrenaline junkies) don't care, since they're in extreme sports paradise and just want to go bungee jumping.

Farl lashes out violently when he feels that his relationship with Amy is threatened. Amy, now becoming fast friends with Lucie, becomes scared about what their relationship might turn into -- especially now that she's pregnant.

Eventually, the Doctor finds out that the interdimensional portal on the mountain houses a monster that feeds on happy fear: adrenaline. Specifically, he finds out when Kai is about to throw him and Lucie into it. The monster has shaped Phobos into an extreme sports paradise on purpose so it can feed. Eventually, it'll break through the rift and become a real threat. Kai knew that the beast is harmed by actual, pure fear, which is why he started the exaggerated myths to protect people and subdue the monster... and when that failed, he started killing people just to drive the Drennies away. When that failed, he set Farl up to become violent and frighten Amy. And when that failed, he figured that dropping the Doctor and Lucie down the portal might create enough fear to do the trick. This earns him a grand What the Hell Hero from the Doctor.

The monster possesses Kai's girl, Eris, and starts talking to the Doctor: explaining to him that his love for saving people, his happiness at rescuing the weak in fearful situations, has fed it to the point of being able to break through the rift. His own adrenaline rush of being the big damn hero has only made the monster stronger, and will become the cause of the deaths of thousands. The Doctor counters that he would never become that sort of person and decides to take matters into his own hands. By taking the Drennies' equipment and bungee jumping into the interdimensional portal.

And he conquers the monster effortlessly by showing it all of his fear. He starts by feeding it detailed memories of all the things he's seen in the past, followed by all the evil he's seen from the future... and as a magnificent final blow, all the things he's afraid he might do one day. The whole Crowning Moment of Awesome takes several minutes, with the Doctor continuously mocking the monster throughout. Eris is killed in the process.

In the aftermath, Kai buries Eris and tries to become a better person; two of the Drennies are prodded to finally admit their man-love for each other; Amy and Farl decide to slowly re-evaluate their relationship, and welcome their new baby into their lives.

The Headhunter was trapped in a cave for a few days and is getting exasperated.