Radio Times, where I work a lot of the time, says this week that it was odd how sister series Holby Blue and Holby City had not seriously crossed paths before, that effectively it was about time. And it said so because this week a Holby City story was resolved in the first of the new Holby Blue series.

I completely disagree.

Now, I’d have watched this new run of Blue anyway, because I liked the last one, and I don’t follow Holby City so I wasn’t the target audience here. But what seems obvious to RT and what I totally agree was a necessary stunt to raise Holby Blue’s profile was a chalice that maybe wasn’t poisoned, but shouldn’t become a regular tipple.

Follow. Holby City’s palest registrar, Jac (Rosie Marcel) is accused of attempted murder in her own series and Holby Blue begins with her being taken into custody. Sold: what Holby City viewer wouldn’t want to see what happened next? But then what Holby City viewer would not already know what would happen next? The only thing that could happen?

Jac is a popular character – or there wouldn’t have been any point crossing her over – and she’s introducing us to a Holby Blue that, it’s hoped, we will like and continue to watch every week. So what’s going to happen? Will the coppers of Holby Blue prove that Jac is guilty and be the bastards who get her put away? Not bleedin’ likely. But if they don’t, if they cannot have any chance of doing that, where exactly is the police drama?

The problem is that characters belong in their own series. Doctor Who pulled off a very rare, I’d even say perhaps uniquely successful trick with the Peter Davison/David Tennant crossover but that had to be in a ten-minute short, it wouldn’t have lasted an episode. And we know that because we’ve seen it: The Three Doctors, The Five Doctors, The Two Doctors, none of them are anything but novelties. I suppose I’m saying there can only be one hero.

I do bridle at the idea of heroes: even Holby Blue whose creators directly stated its characters were heroes has allowed for the lead John Keenan (Cal Macaninch) to be a git savant. (Holby Blue’s “dedicated heroes”.)

But in straight dramatic terms, the protagonist is the protagonist: Keenan is the lead in Holby Blue, although Luke French (Richard Harrington) is strong and will be brought forward more if this show extends to Casualty-like 50-odd episode series. Everything services the protagonist, it’s the way that Sherlock Holmes only ever finds clues that Sherlock Holmes can understand; it’s why nobody ever has any problem whatsoever that doesn’t need a $2m Bell helicopter and its pilot in Airwolf. “My council tax has gone up!” Whop-whop-whop, de-diddle-de-diddle-ee-dee… )

Taking a character out of his or her artificial surroundings is extraordinarily risky. Why does EastEnders struggle when it sends its characters to France or Brighton or anywhere outside the Square? Why do you know to groan when a US series has a special set in the UK? It’s not because the characters are unbelievable or exaggerated, necessarily, it’s because the character is so much a part of its constructed environment. It ought to be fantastic to see them in a new situation because situation is illuminating of character but as much as shows flounder when they do it, we fight them back when they try. There is a wonderful episode of ER called Day for Knight, one of the first shows I reviewed for BBC Ceefax, in which everything is still set in the hospital, all the regulars are there but the entire episode is from the point of view of a brand-new doctor, Lucy Knight. The regulars come out very mildly badly and ER’s fans loathed it.)

You can see the problem most acutely in a crossover like the one that happened between Magnum pi and Murder She Wrote. Honest. “Magnum on Ice part 1” aired on Don Bellisario’s Hawaiian detective show and part 2 was on Peter Fischer, Dick Levinson and Bill Link’s series about crime writer Jessica Fletcher. You’ll never guess where she went on holiday that year.

This aired recently on whatever UK digital channel is churning through Murder She Wrote. Part 1 is typical Magnum and in fact in syndication it isn’t part 1 of anything, it’s a standalone Magnum, pi episode with a pretty rushed ending. As originally aired and on DVD, part 1 has our hero Thomas Magnum (Tom Selleck) being our hero, and part 2 has him not being our hero at all. He cannot solve the crime, he cannot clear his name, it must all fall to Jessica (Angela Lansbury). The lead character of the series always wins: Peter Davison’s Doctor is the one who does all the work in Doctor Who’s The Five Doctors because he was the incumbent.

If that doesn’t happen, the lead character in the host series is weakened, even denuded. If it does happen, the character from the other show is weakened, even denuded.

You don’t have a choice which character is damaged: it is invariably the one from the other show or you’re actually shooting your own entire series in the foot. And you cannot change the outcome of the story: Jessica couldn’t fail to rescue Magnum, Keenan and French couldn’t find Jac guilty.

So I argue that what appears to be a golden episode, a gift from Holby City to its new sibling, is actually murderously difficult. So much so that Holby Blue was gambling with the viewers it already had: I don’t follow Holby City, I’ve no investment in its characters, I liked Blue and could have felt cheated with a substandard episode.

You’ve already guessed that I didn’t feel cheated. I think I watched it more with my writer’s hat on than my viewer’s one but that was probably inevitable given how interesting I think the whole crossover concept is. And there are bits that didn’t work for me: it’s funny how UK series are not as able to use pop music as US ones are, or at least how we are more ready to accept it in American drama than British; similarly Homicide could’ve got away with its police officers impersonating a dog.

What Holby Blue did well, I think, is keep Jac and other characters from Holby City in a little bubble: we predominantly saw Jac in her cell or in the interrogation room. It was the most important story and we never felt it wasn’t, yet minute-by-minute it didn’t appear to get as much time as all the rest. In truth it did, we just didn’t know that until we saw how the other story strands came together and affected Jac’s, but it didn’t seem to get the majority of the time. And yet it didn’t feel cut back, I didn’t feel robbed of the headline story: I don’t know how writer Tony Jordan pulled that off but he did.

And Jac, stuck in her bubble, got to argue with the police and thereby be as strong as she apparently is in City while the police got to be persistent buggers. We were taught how interviews go, seeing them stone-faced asking the same questions of witnesses and not reacting to the wildly different answers, so we knew when they faced Jac that we were seeing a performance. Well, kind of: it was a character-revealing performance, but still not a face-on character study. And though it wasn’t original, having Keenan and French decide which would be the good cop, which the bad, it did work when they seemed to fall naturally into the opposite roles.

Was that a requirement of protecting the show from crossover? French took the lead and was the bad cop, our primary Holby Blue guy was the good one even though we’d been told to expect it to be the other way around. So we like John Keenan but we know he can be tough when necessary. Even typing that sounds cliched, but signals are sent in drama and we receive them.

I don’t know how much we saw in Holby City but within Blue the key detail of the case was held back to the last second that it could be and then tried to be hidden. But as soon as we knew Jac had seen a patient, we knew that patient was the murderer.

Similarly, equal weight was given to what I believe was a new Blue story involving a woman who had been beaten up. I think it should have been obvious she was the patient, but I didn’t see that, I didn’t make the connection. I would rather the reveal had been more than coincidence – Jac was being processed at the custody desk when she happened to see this patient leaving the station on a security monitor – but it was a surprise to me.

And that tied off the whole Holby City storyline: Blue just needed to do what it could to keep us. So we saw several police storylines, we were re-introduced to all the returning characters and most of the rivalries, there was sex and intrigue to set us up for coming back to see episode 2.

And, quite brilliantly, there was a birth, an overdue baby.

This must be just about the sole medical story Holby Blue could possibly come up with, and it came up with it for the episode that crossed over with medical drama Holby City.

You have to applaud and compared to any crossover episode I’ve ever seen, Holby Blue Meets Holby City got away with it.

But there are teeth and skin marks all over it.

I’ll bet you money Tony Jordan did not work this all out on a graph before writing the script. He’s too experienced to have not seen the pitfalls. But if he did write it by the numbers, solution-by-solution, then he’s annoyingly good at hiding the scaffolding.

William