The Twelfth Doctor once investigated the existence of a type of creature evolved to be perfect at hiding, which Clara Oswald referred to as "hiding creatures". (TV: Listen [+]Loading...["Listen (TV story)"]) The Doctor was inspired in this quest by a poem. (WC: Listen [+]Loading...["Listen (webcast)"])
The Doctor and Clara encountered a figure at West Country Children's Home who may have been one of these creatures. (TV: Listen [+]Loading...["Listen (TV story)"])
A group of adventurers may have also investigated the hiding creatures. If the creatures were real, one of them might have revealed itself to one of the adventurers and told them that it knew everyone's secrets and could share them for a price. (GAME: Listen [+]Loading...["Listen (game)"])