The eBook is written by Patrick Ness, author of the Chaos Walking trilogy and A Monster Calls, and features the Fifth Doctor and his companion Nyssa, played in the TV series by Peter Davison and Sarah Sutton respectively.
A synopsis has been released for the story:
"In 1945, a strange new craze for Truth Tellers is sweeping the kids of small-town America. The Fifth Doctor and Nyssa soon arrive to investigate the phenomenon, only to discover that the actual truth behind the Truth Tellers is far more sinister than anyone could have imagined…"The eBook will be released on 23rd May, and will cost £1.99. Tip of the Tongue, alongside the ten other eShorts published throughout the year, will be included in a paperback anthology released on 23rd November.
[Source: Doctor Who TV]