'Shadowmind', written by Christopher Bulis, features the Seventh Doctor, Ace and Bernice.
Back Cover Blurb
Arden. A planet of hills and streams and forests. Peaceful. Friendly.
'Ther is no indigenous intelligent life there,' 'What is there then?' the Doctor said. 'It's o new colony world, Doctor. We started developing it three years ago.'
But there is something on Arden. Something that steals minds and memories. Something that is growing stronger. Something that can reach out to, the regional stellar capital, Taingaire - where the newest exhibit in the sculpture park is a blue box surmounted by a flashing light.