Recap: Big Finish Doctor Who 037 The Sandman
The Sixth Doctor and Evelyn arrive on one of the ships of "The Clutch", a fleet of interstellar craft that are constantly on the move, never settling on any planet. The Doctor is there to pay a visit to the resident Galyari merchant clan, a race of lizard-like Space Jews
that were, in their past, very warlike. They are held in check by fear of The Sandman, a terrible legend from their past. The Sandman steals the skins of Galyari children and weaves them into his coat, and it is blinding pain, or even death, to look at him.
To Evelyn's great surprise, the Doctor is the Sandman of Galyari legend, come to strike fear into them once more.
In the end, it turns out that the Doctor is indeed the one who helped win the war against the Galyari, and destroyed the racial memory artifact that made them so warlike in the first place. Without their racial memory to cling to, and with a crippling fear of the Doctor's wrath implanted into their collective consciousness, they instead became merchants, incapable of even understanding evil. As for their other legends about him: it turns out that the Galyari were once able to camouflage themselves, and able to recognise camouflaged members of their own race due to hypersensitive vision. Although they've evolved past nigh-invisibility, the enhanced vision stayed part of their biology, and they're literally
allergic to the Sixth Doctor's fashion sense.
In the end, the Doctor defeats the real murderer-slash-skin-thief, and the Galyari find out that they can now live without fear.