How faithful is His Dark Materials season 2 to the books?

And the good news for fans is that the second season appears to be doing the same thing again, with the story of Pullman's sequel The Subtle Knife presented largely unaltered, save for a few minor changes.

"There isn't sort of that major shock [like Will appearing in series one]...but there's a series of micro-shocks that together probably challenge the foundations in a more interesting way," writer Jack Thorne told RadioTimes.com and other press when asked about changes.

"Our thing is always how can we tell Philip's story best. We are not trying to do something different from the books. We are only ever trying to feed the language of TV into these books.

"And so sometimes we do step away and do different things - but always we're going back to the text and saying how does this help us tell his story best."

But what are the major changes? Here's some of what we've spotted so far.

The Magisterium

As was the case in series one, the storyline surrounding the Magisterium has been expanded from the novel, with the character Father MacPhail – who doesn't actually make a book appearance until The Amber Spyglass – given much more to do in particular.

The series introduces a schism between various factions of the Magisterium, as different people seek to wrestle control over the organisation, while we also see them wage war with the witches.

Writer Jack Thorne has gone into detail about why he's decided to put more focus on the Magisterium in the show. He said, "It's hard to talk about... because there's a thing that happens in series three, as we've got it in our heads, that sees Father MacPhail do something quite extraordinary, and quite desperate.

"And that question always intrigued us. It was something that we always wanted to itch at. So we brought him forward into series one and established him as a very solid member of the magisterium - someone who could be relied on in the magisterium.

"And through series two we see him transform into a leader, and we see him making moral decisions which shape him as a person. And we're all building to that moment in season three where he steps over the edge into something quite, quite dark."

Another new addition is a conversation between Mrs Coulter and Asriel's manservant Thorold which takes place at the end of the episode, in which he informs her of Asriel's activities and the events that occurred at the end of Northern Lights. Thorold does appear towards the beginning of The Subtle Knife – but he speaks with Serafina Pekkala, not Mrs Coulter.

The Witches

Another area in which the show has significantly expanded on the books concerns the Witches, including Serafina Pekkala and Ruta Skadi

Explaining why changes had been made to the witch storylines in the series, Jack Thorne credited some of the writers new to the team – including Francesca Gardiner, Sarah Quintrell and Namsi Khan – who he said pushed him to do more.

"They really did bring scope and challenged us in lots of different ways," he told RadioTimes.com and other press. "The witches were something where the writers' room said that the direction I wanted to take them in wasn't quite deep enough. And they took them, and I love what's come out as a result. It's absolutely incredible."

Among the changes, the biggest is probably the increased role given to Ruta Skadi. In the opening episode of the series a witch is being tortured for information by Mrs Coulter and the Magisterium, and while a similar scene does take place in the novel, a number of changes were made for the show.

In the book, the scene takes place on a ship rather than a submarine while the Cloud-Pine torture method Mrs Coulter uses is also an invention for the show. And then there's the small manner of the witch's identity – she is unnamed in the book, but referred to as Katya in the series.

The biggest change here, though, relates to the rescue mission staged by the other witches. In The Subtle Knife, Serafina Pekkala had been hiding throughout the torture scene before summoning Yambe-Akkka (the goddess who comes to a witch before they die) and killing the witch in an act of mercy.

In the series this plays out very differently: Ruta Skadi rescues the witch against Serafina's orders, battling her way past several Magisterium officials in the process.

Will and Lyra

Perhaps the biggest change made from the opening sections of The Subtle Knife relates to Will Parry (Amir Wilson), and technicaly already happened in season one. In the book Will is introduced in the first chapter, having not appeared in Northern Lights, but of course, this is different in the series: the first parts of Will's story were already told in series one and so there is no need for them to be repeated in the series two premiere.

Instead, we see Will and Lyra's first encounter from Lyra's perspective, seeing her traipse through some forest terrain and hiding out in a cave before she arrives in Cittàgazze, with Will surprising her in a shop and the two briefly sparring.

Beyond this, the storylines for the two main characters are left largely unaltered, although there are a few small differences.

For example, Will has a smartphone (reflecting the slight change in the time period the series is set in), while we also see a scene in episode two in which Will visits his grandparents – of whom he was previously unaware of – who inform the police of his whereabouts. That scene does not occur in the book, instead, Will learns from an archaeologist that a journalist who had been asking questions was actually one of the agents who had been bothering his mother.

Other character changes

There are a number of other character changes worth pointing out. First of all, a number of book characters who do not appear in The Subtle do have a role in series 2 – including Father MacPhail, witch consul Dr Lanselius and armoured bear king Iorek Byrnison.

Meanwhile, we also see some meetings between characters who never come face to face in the books, including an episode two meeting between Mrs Coulter and Asriel's manservant Thorold and a few others we won't spoil ahead of time.

Then there's a slight difference regarding the children Will and Lyra meet in Citagazze. In the book, they meet a boy and a girl named Paolo and Angelica, but in the series, there are two girls – Paolo being replaced by Paola.

Casting director Kahleen Crawford explained the reasons behind that particular change to RadioTimes.com, saying that it was a result of the casting process.

"We just had an embarrassment of riches in the casting process," she explained. "And when it came down to it we had some really great younger brothers to play Paolo – but ultimately we had these two girls Ella and Bella... who were so strong in their performances that, if I’m remembering correctly it was essentially decided that their parts should be made bigger, and there would be more for them to do on-screen."

Read more about the His Dark Materials cast, James McAvoy's cut episode, the His Dark Materials release schedule and the His Dark Materials age rating, plus find out where His Dark Materials is filmed, including the scenes set in Cittàgazze. And why not look at our latest His Dark Materials review?

His Dark Materials airs on BBC One on Sundays at 8:10pm. Want something else to watch? Check out our full TV Guide.