Heroes of Sontar, by the reliable Alan Barnes, is the better story of the two. At first it seems a rather peculiar and not necessarily successful attempt at a humorous twist on the Sontarans, as a bunch of deadbeat veterans are sent on a mysterious mission to a planet deep in Rutan space. But this being Alan Barnes, all is not what it seems, and Janet Fielding and Mark Strickson in particular get some good moments as Tegan and Turlough as the Tardis team work out the awful truth behind the apparent absence of sentient life on the planet. Poor Sarah Sutton is not as well served as the older Nyssa, though she gets some sentimental moments with Tegan near the end, and I was not wild about the characterisation of the Doctor. But I was much more impressed by Barnes' ringing of the changes on the Sontarans here than by, say, Colin Brake's retake on the Judoon.
I was less wild about The Sentinels of the New Dawn by Paul Finch, which turns out to be a sort-of prequel to the Lost Story Leviathan, adapted by Finch from a script by his father Brian. Liz Shaw, having recently left UNIT, summons the Third Doctor to Cambridge to help her with a case of timewarping machinery which turns out to have political implications for the year 2014. It didn't especially grab me, though Caroline John is always good to hear; a slightly personal grumble is that I wish people who actually know Cambridge would write Liz Shaw stories - time travel experiments would surely be a bit more likely to be done at the Cavendish rather than at DAMTP as here, DAMTP not being well known for its experimental facilities (or indeed inclinations). Maybe things are different in the Whoniverse. (I recently became familiar with the term Brit-picking; is there a specifically Cambridge version of it which I suffer from?)