April Books 7) K9 and the Time Trap
He had been a great engineer. It was he who had created the system that gave the Time Lords time-travel. 'I harnessed the power of a thousand suns for them,' he said. 'They made me emperor - then plotted to destroy me, and marooned me here! They think I am trapped in this crimson bubble of time,' roared Omegon, 'but soon I shall have my revenge!'K9 deals with him pretty rapidly after that, but it's obvious who Omegon is meant to be, especially considering who wrote The Three Doctors. (For other Omega revivals see the excellent Big Finish audio Omega, and Arc of Infinity which I'm less wild about but will reach in my rewatch very soon.)
April Books 8) K9 and the Beasts of Vega
April Books 9) K9 and the Zeta Rescue
The plot is a bit unfocussed: K9 finds a vast prison ship and an attractive young prisoner called Dea (see left); he frees her, and she explains that they are witnessing the last stages of a war between the Telians and Megallans; K9 and Dea then watch as the two sides' leaders mutually destroy each other. K9, having not actually done anything to resolve the crisis, then stays behind to help Dea care for the remaining victims, explaining to the Time Lords on his return that he was aiming to improve his "understanding of the humanoid race", though with negative results. It's an interesting counterpart to the previous book in that K9 appears to feel that his lack of emotions is a potential disability after all.
April Books 10) K9 and the Missing Planet
The last is the most political of the books: K9 is called in to assist the capitalist, colonialist leadership of the heavily polluted planet Tellus (or, as we call it, Earth) to track down a missing colony.
K9 gets caught in a timewarp and finds the missing planet and miners, who are constructing a new Eden with animals from all periods of geological history which they survey by balloon. Votri, the miners' leader, begs K9 to keep his secret; and K9 does so, in defiance of his orders, reporting back to Gallifrey only that the planet has "disappeared from the universe as we know it".'It's not there,' snarled the president [see right]. 'It should be there and it's gone. The whole planet, gone. We own that planet, we've invested billions in it, and we need its raw materials to fuel our power plants and supply our factories. Tellac Inc wants it back. Apart from that they tell me it's playing havoc with navigation ... 0h, and there are a dozen families missing too. Miners, it says here. You better get it back!'
A couple of general observations. Martin is clearly keen on using real star systems - the first book features Rigellian spaceships, the second Vega, the third Zeta Cancri, and the fourth Earth. He's also keen on Greek letters - Zeta and Omega/Omegon, also the Doctor's Gallifreyan name of Theta Sigma, first used in The Armageddon Factor and referred to again several times here. I note that that each book has precisely one other named character (Omegon, Professor Romius, Dea, Votri) which is a bit of a weakness.
However, I do like the mini-character arc of K9 getting to grips with humanity over the last three books; it's an old sf trope, the robot who deals with these puzzling humans, but I had not really seen it done before for K9. For what they are, this a very pleasing set of books.