June Books 3) The Taint, by Michael Collier
Nineteen adventures into the Eighth Doctor series, and he finally gets a new companion in the shape of Fitz Kreiner (I have seen a claim somewhere that there are more stories with Fitz than for any other companion), picked up on a visit to 1963 in which his mother is killed by the gruesomely horrible Taine, leech-like internal parasites feeding on brainwaves. The writing is decent enough; I was a bit startled by Fitz's unreconstructed early Sixties predatory masculinity directed to Sam, having only read later stories in the range; presumably he mellows out in the course of the series.