I think this is the last in the series of short Who books by well-known authors published this year, which had a couple of earlier hits with Trudi Canavan’s Salt of the Earth, Jenny Colgan’s Into the Nowhere and A.L. Kennedy’s The Death Pit.
This is certainly a hit. Harris was born in 1964, so Jon Pertwee was very much her Doctor, and here she gives the Third Doctor a final adventure as he flees, poisoned, from Metebelis Three on his last journey to UNIT headquarters, sidetracked on the way to help out a threatened planet and a dying girl. It packs an unexpected punch and I was very moved by the end. The Time Trips series goes out with a bang.