Big Finish Doctor Who/Recap/S5/E08 The Perpetual Bond/CC

Steven and the First Doctor, fresh and raw from The Daleks' Master Plan, land in 1966 London. The Doctor thinks this is a kindness after all the death they have recently witnessed, and Steven suggests they go visit Ian and Barbara since the opportunity has presented itself.

But on their way, they are distracted by the sight of a humanoid alien boarding a bus. None of the native Londoners seem to notice it, so the Doctor and Steven tail it to a stock exchange where they lose the alien, but meet a young trader by the name of Oliver Harper who recognises it. Oliver is in a hurry to get on his way, but the Doctor convinces him to stay and help them out.

They split up to try and uncover the aliens' plans: The Doctor to talk to Oliver's boss, and Oliver and Steven to the stock exchange floor to root out the aliens themselves. The plan, predictably, isn't all that benign and the Doctor and companions make efforts to stop it.

Meanwhile, Oliver has a secret of his own: He's on the run from the police, and the TARDIS crew provide him a perfect opportunity to escape their closing net.

This is the first Companion Chronicle to introduce an ongoing companion, as Oliver Harper continues to travel with the Doctor after this story ends.

Tropes:

 * Dark Secret: Oliver is determined the TARDIS crew don't find out the real reason he wants to leave Earth with them.
 * Hoist By His Own Petard: The Fulgurites, the
 * Invisible to Normals: The Fulgurites. Oliver can only see them once he realises he can't be a part of the traders' world now the police are onto him.
 * Jumped At the Call: The Doctor, when he sees an alien in 1966 London that shouldn't be there. Steven decides that chasing a mystery takes the Doctor's mind off all the recent deaths far more effectively than visiting old friends would.
 * Laser-Guided Amnesia: Used on the traders to make them forget the stir Steven and Oliver cause in an attempted escape.
 * Made a Slave: The entire story revolves around the Doctor