Just how exactly did Peter Jackson and Andy Serkis’s shocking plan to return to Middle-earth with the forthcoming The Lord of The Rings: The Hunt for Gollum come about? Let us imagine the duo kicking back in Jackson’s Hobbity New Zealand pad with a good batch of Longbottom Leaf, several cases of miruvor wine recently delivered from Lothlórien, and plenty of seed cakes and cold chicken. Conspicuous by their absence from the party, however, unless something distinctly fishy is going on, are Viggo Mortensen (AKA Aragorn, AKA Strider, AKA King of Arnor and Gondor) and Ian McKellen (AKA Gandalf, AKA Mithrandir, AKA that bloke with the pointy hat and the fireworks). Because neither seems to have been so much as consulted about the new movie before it was announced to the public.

This is only strange if The Hunt for Gollum does turn out to be what everyone expects it to be, a big screen take on a minor section of JRR Tolkien’s sprawling fantasy tome that was only left out of Jackson’s Oscar-winning turn-of-the-century film trilogy because there was really no reason for it to be left in. The new movie is widely expected to cover the period in which Aragorn, who has been charged by Gandalf with the task of finding out what happened to Gollum after Bilbo’s encounter with the hideous creature beneath the Misty Mountains in The Hobbit, finally gets his hands on the rotten miscreant in the Dead Marshes and drags him before the elves of Mirkwood. It’s mentioned briefly in the books at the Council of Elrond, and lightly passed over in the same chapter of the movies.

If it turns out that The Hunt for Gollum really is about this minor segue – and honestly, how could it be about anything else? – it seems remarkable that nobody thought to tell McKellen and Mortensen what was going on, even if only to prepare them for the fact that, at 85 and 65 respectively, they might be better off priming themselves for replacement by younger actors. If that is the plan, the team behind this most unexpected new episode are probably regretting not communicating it earlier. For this week McKellen told the Times he would be quite up for starring as Gandalf once again – if he lives long enough.

This follows Mortensen telling GQ last month that he would also be interested in returning as Aragorn provided “I was right for it in terms of, you know, the age I am now and so forth”. Both actors implied they had not been told anything about the new film before it was revealed to the public, with McKellen saying he had heard only “stirrings in Tolkien land”, while Mortensen said: “I don’t know exactly what the story is, I haven’t heard. Maybe I’ll hear about it eventually.”

Meanwhile, and despite the fact that two of the major stars who would be expected to appear in it have no idea what’s going on, this thing is happening. Variety reported last month that Serkis will direct and star as Gollum (via mo-cap), with Jackson producing alongside his regular team of Fran Walsh and Philippa Boyens, for studio Warner Bros. The whole thing feels a little like film-making by press release, where a small band of people decide something is a good idea, and everyone else is expected to jump in a barrel to Lake-town without really looking where they are going.

Of course, this could all be a case of smoke and (Galadriel’s) mirrors. Maybe Gandalf and Aragorn have really been on board this thing from day one, and Jackson is just holding back the big announce until our sense of nostalgia has built to fever point. They’ve all been primed to pretend they know nothing about it, when the truth is that the hallowed pair will soon be back looking considerably younger and more sprightly than they even did in the original movie triptych, thanks to the magic of technology. If you thought it was impressive watching 60-something McKellen take on giant cave trolls in The Fellowship of the Ring, just wait til you see him going full Harrison Ford in Indiana Jones and the Dial of Destiny on some poor Easterling orc at the age of nearly 90.

Except that’s the thing about The Hunt for Gollum. If it is what we think it is, there may not be a lot of heavy action sequences to film, so perhaps McKellen won’t need to get his kung fu on after all. Mortensen? Trying to convince us that the sexagenarian fellow we see on screen these days is the same dashing Númenórean we all melted at more than 20 years ago might be much harder going. Let’s hope the mo-cap “ghosting” machines have been warmed up for months and are humming away like a Hobbit’s stomach before second breakfast – they are going to be needed.