That was a decent book! It's not a masterpiece to survive the ages or anything, but it's perfectly respectable and one of the few Bulis books I actually remembered. That's partly because of its attention-grabbing high concept, but also because in its unobtrusive way it's fairly good.
I like best its use of Peri. With the Doctor busy preparing to become a gladiator (albeit with a radio link to keep him in on discussions), Peri ends up taking charge of much of the story. I like what happens with her metamorphic problem, as you can see from the birdwoman cover illustration. She's practically the book's real hero, not the Doctor.
The Bulis's 6th Doctor isn't as strongly portrayed. There's a time-reversal effect which occasionally regresses him to previous incarnations, which is a cute idea which backfired when sometimes I couldn't work out whether I was meant to be reading about Jon Pertwee or Colin Baker! Despite a few token lines, this is the kinder, gentler Colin several years before Big Finish. He's a bit bland, to be honest. However he gets plenty to do and is always Doctorish, so on that level the portrayal works.
As an aside, it's weird to see a multi-Doctor Colin-era story with Hartnell. The Virgin MAs tended to be period pastiche, especially when written by the Bulis, so it feels odd to include a story element that would have been unfilmable in 1985. That's hardly a fair criticism, but it's how I felt. Maybe it's because the idea seems slightly wanky? In addition at the end we see the creation of a mirror-Earth which reminds me of Mondas's mirror-image continents. Was the Bulis trying to sneak in a Genesis of the Cybermen, just like the possible Genesis of the Movellans in A Device of Death? On reflection I don't think this can be Mondas, but it made me wonder.
I like this subtle approach to continuity, though. For example, the TARDIS is equipped with Hartnell's furniture. Even in the Virgin era of Hinton, Lane et al, the Bulis was keeping its fanwank to delicate touches instead of hammerblows. Nice one!
The book's biggest problem is its apparent alternate universe. My interest started recovering halfway through when we learned the real situation, but even so it took me a while to care about the local politics. I'm not always gripped by real-life Imperial Rome. Giving me an unreal substitute wasn't a good move. The characterisation is variable... some of the locals are dumb stereotypes, e.g. comedy tomb robbers on the run from Terrance Dicks, but I liked Ptolemy. He's not deep, but he's sympathetic. The Bulis seems to have a knack for such characters even in otherwise undistinguished books, as with Amelia Grover in Eye of the Giant or Max the synthoid in A Device of Death.
This is a decent book with some interesting themes (see the title) and a fun set-piece or two. I enjoyed the Doctor's gladiatorial fight, with which the Bulis sensibly doesn't even try to scare us. We know the Doctor won't die. We only want him to entertain - and he does. The book isn't particularly well executed, but its prose and characters are passable enough not to hurt the story. I couldn't say that this book cried out to be published, but it does its job and it's better than many other Doctor Who novels I could name. I enjoyed it.
After seeing Cleopatra's pleasure barge in Ancient Egypt, Peri asks the Sixth Doctor whether they can go somewhere where they can interact with the people of this time, but as the Doctor is dematerialising the TARDIS, it is hit by the presence of an alien and when the ship lands, they find themselves in Rome twenty five years later than when they were in Ancient Egypt. But this is a Rome where they have invented electricity, radio and airships, which the Doctor can't believe. But as they begin to explore the tomb they find themselves in, something strange is happening to both Peri and the Doctor. Peri seems to be reverting to the birdlike creature she became on Varos, and is shocked when something bizarre happens to the Doctor.
Christopher Bulis' 'State of Change' is set in the gap between Revelation of the Daleks and The Trial of a Time Lord, and Bulis takes this opportunity to develop the relationship between the Doctor and Peri into what they should always have been - companions who actually seem to like each other and don't spend the entire story arguing with each other.
The plot has a very interesting idea at it's heart. What would the world have been like if the Romans had developed modern technology? The cover to this novel by Alister Pearson demonstrates this well with a depiction of a Rome with power stations bellowing black smoke into the air, tall radio transmitters and a huge airship hovering over the city. The guards of Rome carry rifles and pistols around, and they've even been developing atomic bombs as well.
One of the main sub-plots revolves around the battle for leadership between Ptolemy Caeser, son of Cleopatra and Julius Caeser, and his younger half siblings, Cleopatra Selene and Alexander Helios, the children of Cleopatra and Mark Anthony. Ptolemy has become Consul of Rome, but has been deeply affected by his year long visit to the East, Alexander Helios has been made Dictator of Rome and is manoeuvring himself into position to become Emperor and Cleopatra Selene is the Queen of the East, but wishes to exert more control over Rome, and is plotting against her brother. This plot for the most of the book actually takes to the foreground and pushes the Doctor's attempts to find out how the world changed like this into the background. This idea of pushing the political aspect of Rome works well here, and Ptolemy's attempts to increase his favour among the masses is very well done.
The actual reason for how this change occurs is a little bit disappointing. It isn't the actual world which has been changed, but the clue as to why it has is revealed by the fact that the Oracle of Alexandria happens to be an exact replica of the TARDIS console. When this is revealed, Bulis does manage to create a real sense of surprise, and manages to convey well the Doctor's shock at discovering this. There are clues about what is happening to the place that the Doctor and Peri find themselves in throughout the book. This leads to some memorable sequences. Peri begins to change into the birdlike creature that she became briefly on Varos and revels in her new found abilities, such as being able to fly and increased strength and agility, and the Doctor has some retro-regeneration problems with exposure to the surrounding area causing him to regenerate back through his previous incarnations and it is a shock when Peri finds the Doctor with the face of the Fifth Doctor. Although this idea is a novel one, thankfully Bulis didn't use it throughout the novel, with the Doctor devising a device to ensure that he maintains his current form. That said, one of the most memorable moments comes when the Doctor has broken into the building containing the Oracle, and faced with an attacking swordsman he calls upon his previous incarnations to help him out. The ideas of the Fifth Doctor to play a straight bat and the Fourth to offer him a jelly baby are priceless. But when the Third Doctor's personality takes over, the expert swordsman quickly defeats his opponents with a combination of swordsmanship and the use of the word 'haa!' which infuriate his opponent.
The characterisation of the Doctor is excellent, with the Sixth Doctor being less bombastic than he appeared on the television, but still showing a little of the superiority that he exhibited. The strength of concern that he shows for Peri when he believes she may be enjoying her transformation too much, which could have serious consequences for her mind upon her return to normality, is wonderfully conveyed and it demonstrates the depth of friendship that the Doctor has with Peri which wasn't always evident in their television adventures.
Peri herself spends much of her time transformed into a birdlike creature, which upon the first time he sees her, Ptolemy believes her to be a harpy. This works quite well within the context of the book, but it does mean that Peri spends a lot of the novel either in the TARDIS or the tomb that the TARDIS materialises within. Peri's acceptance of her transformation is believable, if improbable. The story behind how the Oracle came into existence, and thus how the technological advances were able to occur, all seems to be wrapped up within a few pages at the end. The identity of one of the Villains is revealed to be a television one, but the inclusion of the Rani feels unnecessary, although without her involvement the whole story wouldn't have begun. She demonstrates her character traits well - the ability to take on disguises and the use of ordinary people to accomplish her schemes with disregard to them - and it does fill in how she escaped her fate in The Mark of the Rani. Bulis' own characters are good on the whole, with Ptolemy Caeser being the best one, although some of the others such as Cassodorus, the thief who gets roped into running Ptolemy's campaign, is noteworthy.
Overall, State of Change is not the best Missing Adventure there was, but it does have a lot of redeeming qualities. It's well written, interesting in concept, and is basically an enjoyable lightweight novel, with good use of the Sixth Doctor.