SPOILER ALERT: Do not read if you have not yet watched “Cornelius Ruck (No. 155),” the 12th episode of “The Blacklist” Season .

Viewers that needed a bit of a respite from the real world on Friday night probably embraced the light-hearted nature of “The Blacklist’s” “Cornelius Ruck” episode, a concluding installment to the previous week’s “Victoria Fenberg (No. 137).” In it, Red (James Spader) traveled to an isolated island to reunite with the group of bandits — including a former flame named Cassandra (Joely Richardson) — who stole a set of valuable caskets and who were now trying to cash in with an unidentified buyer.

The Red-centric episode was a departure from a typical “Blacklist” episode, with its lighter tone and Agatha Christie inspired island-mansion backdrop, as each of the thieves were being picked off one-by-one by an unknown murderer.

“When the first half of the season ended Red was in a really good space. He is under the impression that Katarina Rostova is dead and his concerns for Liz’s well-being are allayed,” executive producer John Eisendrath tells Variety. “In many ways he’s more confident that his role in looking out for Liz and Agnes has been successful. So he’s in an upbeat place and, as a result, we felt like to underscore that this would be a great time for him to take care of some business that was unrelated to the mythology of the show and the weight that he often carries. It’s an exciting but ultimately light ending.”

Here, Eisendrath and executive producer Jon Bokenkamp discuss crafting the episode, the importance of Cassandra’s character, and what it all means for Liz and Red.

How inspired by Agatha Christie, or the success of “Knives Out,” or any of those classic whodunnits were you for this episode?

Bokenkamp: If I recall right, we were breaking this right before “Knives Out.” I think the trailers were out because I remember talking about it afterwards. The show can become awfully dark especially with all the questions that the audience is grappling with. It felt like after ending on this note where we left viewers in the fall, we really did just want to come back and remind viewers that the show can be a lot of fun too — even if it’s a bit of a murder mystery. The show has a lot of different hats that it wears. It can be a sci-fi show, or a dark thriller, or funny. There’s probably a little more Agatha Christie in spots and then there was inspiration maybe from the movie “Clue” a long time ago.

Eisendrath: Though our show is a crime show, it’s not really a whodunnit. Going into every episode from the beginning it basically tells viewers who the Blacklister is. This is like “Clue” or an Agatha Christie story, and we really don’t do those often. It’s a fun departure. We often introduce fun and comedic parts of Red’s past, but occasionally we like to dip into his personal life and explore the relationships he had in the past that could tell us about who he was before the show. Certainly the part played by Joely Richardson fits into that category. Fans see this relationship that could have been something more but for his obligations to Liz. Now he feels his obligation to Liz is mostly complete in terms of her safety and he could potentially go off and be with a woman who he had a great affection for, but still he picks Liz.

She kind of made that decision for him in the end, no?

Eisendrath: Well she picks for him only after she realizes that Liz is where his obligations really lay.

In a Red-centric installment that’s meant to inform the character like this, does James Spader become more involved than he is in a typical episode?

Bokenkamp: I think it’s business as usual. We always have lots of conversations about the development and the story and the various characters and who they are. One of the crazy things about this episode story-wise is we shoot in Manhattan and yet we’re telling the story of how Red and some of the people from his past were gathering on a mysterious island in the middle of the ocean. That’s kind of hard to produce. And so there were more issues like that that we were dealing with in terms of getting the episode on its feet versus it being so heavy with James.

How important was nailing the mansion and the atmosphere to get the tone of the episode right?

Bokenkamp: That’s all New York; they do a really great job. There’s snow, there’s airplanes and float plans, and yet it’s a contained episode and we’re meeting a lot of different characters. It’s one of the things that’s fun about “The Blacklist” — it’s not just the police precinct every week. We go to these fun weird, strange, different places and this is one of them. Seven seasons in we’re trying to find things about Reddington that we didn’t know and here we are meeting a crew that he did a heist years ago with and meeting those characters is what makes it fun for us as writers to just explore his character. But it was definitely an out-of-template story for us.

How did Joely Richardson come about?

Bokenkamp: We knew that there was going to be somebody from Red’s past that we wanted to bring back and we would meet somebody who he maybe had had a relationship with or was somebody who was close to him, specifically because of that ending where she needs to let him go and suggest he stays with Liz. When we started talking about people, Joely was brought up very early on and we were huge fans. We were lucky to get her, they felt like they had a real history together. It was earned.

To escape, Red had to pull off another small miracle — after seven seasons how do you find inspiration to write those scenes and keep these kinds of escapes fresh? Is there a running list of ideas?

Eisendrath: It’s mostly just trying to surprise ourselves. It made us laugh in the room, the idea of the sword from the swordfish. That was something that we definitely had not done before. And it felt like that was at least a good way for him to deal with the guy he was about to be shot by.

Bokenkamp: I wish we had a list we could draw from. Sometimes it’s just trying to imagine where he is, or where any of the characters are. What might be in an estate that could be used. Like a swordfish over the mantle. In this case that felt fun and in the spirit of the episode. It was light and merited.

With Cassandra leaving Red and Red realizing he still wants to be there for Liz and Agnes, does that shift their relationship at all?

Eisendrath: At the moment in some ways Liz is the one who is not being honest with him because she knows Katarina is alive and not telling Red that she’s giving her mother time to hunt down whatever she’s looking for. We go back and forth in terms of who is ahead between Red and Liz, and who knows what. Right now Liz is ahead of Red and so Red is really in earnest in his feeling that they’re in a good place. And the Joely Richardson character was in part designed to underscore that. He really did have a good connection with Cassandra — they were going to go off and get together — but he didn’t because Liz was in danger. It was our desire to really bring them close together from Red’s point-of-view in particular, in anticipation of the craziness that will come later on in the year.

“The Blacklist” airs Fridays at 8 p.m. on NBC.