The storyline sees one of Chantelle's patients - a pregnant woman named Sarah - take a sudden turn for the worse in theatre, ultimately being declared brain-stem dead in heartbreaking scenes.
Soon afterwards, the hospital's team must make a difficult decision over what to do next - turn the life-support machine off and lose the baby, or try to prolong Sarah's life mechanically until the baby is more developed.
When Hanssen calls Chantelle up to an MDT meeting to have her say on the situation, her opinion isn't shared by the majority of the doctors - but can she bring them round to her way of thinking?
Digital Spy recently chatted to Lauren Drummond, who plays Chantelle, to hear more about the storyline and her time on Holby City so far.
This week, we see that Chantelle is feeling unsure of her abilities as a nurse. Why is that?
"I think it's because she's up for the permanent role and also because Serena has come into the hospital. For a little while it had just been Chantelle, Ric Griffin and Malick. Ric really gets Chantelle - he's sensitive towards her, he knows what she's like and acts accordingly!
"When it comes to Serena, she and Chantelle are still getting used to each other. Chantelle gets on easily with everybody, but I think she's feeling like she has to prove herself at the moment and putting pressure on herself."
Ric decides to boost Chantelle's confidence by assigning her to difficult patient Sarah - a pregnant woman who is blocking certain tests that might endanger the baby. How does Chantelle feel about the challenge?
"I don't think Chantelle sees that as too much of a problem, as she relishes in those kind of challenges. She actually doesn't really see it as too much of a challenge, because she's a people person and that's where her confidence is.
"The difficult patients for Chantelle are people like Dan's dad, because she can't stand rudeness or anyone being impolite. But Chantelle is quite excited about the challenge of looking after Sarah, especially with a baby being involved."
When Sarah takes a turn for the worse in theatre, Chantelle gives her husband James some false hope, doesn't she?
"She does. Ric warns Chantelle that things aren't looking good, so under no circumstances must she give James any false hope. However, James starts pushing her and asking for answers. She tries really hard to deflect the question and says that Mr Griffin will explain everything, but in the end she does give him false hope.
"Chantelle's point of view is that hope hasn't gone yet - she is naturally quite a hopeful character. Although she didn't want to say the wrong thing, this man's at breaking point and she can't watch somebody fall apart. She doesn't intentionally mean to lead him down the wrong road, but it does turn out to be a mistake."
Pictured: Chantelle with James.
When it becomes clear that Sarah will never wake up, what does Chantelle say in the meeting to discuss the baby's future?
"Chantelle's point of view is to go against the odds, really. There is a strong argument for the baby not to be given a chance, because the statistics aren't good for a positive outcome. However, Chantelle does her research and finds out that even though the odds aren't high, there is a possibility of the baby surviving. She fights for that possibility, because she has been on a level with Sarah and she knows how much this baby had meant to her."
We don't want to give away too much about what happens next, but was this one of your favourite episodes to film?
"It was! I'm very protective of Chantelle and I don't want people to think that she's just a pretty face. There's a lot more to her character, and I think it's important to show that.
"At the same time, I don't think this story will be a huge turning point - Chantelle won't suddenly become a really serious nurse all the time now! But I think you can still be a light-hearted character, while also having the integrity and the skill that is required. Maybe this is one of the times that you get to see another side of Chantelle."
How do you think Chantelle could improve further as a nurse?
"I think it's something that will come with age. Everything comes with experience and this is her first nursing job. I don't think she'll ever be a business-minded nurse - I think she'll always be for the patients. But I think she'll probably start to understand the hospital policies a bit more.
"What ruffles the feathers of people like Serena is that it takes a while for Chantelle to stick to hospital policy, because she goes with her heart."
You've been at Holby City for over a year now. How have you found your time there in general?
"I love it at Holby - it's a great place to work, the production values are very high and everyone there is very talented, so it's a great place for me to work and learn. It's a lovely job!
"Sometimes when you play a character in a continuing show, you can end up feeling like you need a bit more variety. But Chantelle is so bubbly and so fun to play that it's one of the best roles I've had. It's been a really fun one to do."
Pictured: Chantelle at the MDT meeting in tomorrow's episode.
How long did it take to settle in at Holby when you started there last year?
"About a week! (Laughs) Everyone accepted me and was really lovely and welcoming. Funnily enough, there's a connection between Tina Hobley and myself, as our grandmas are first cousins.
"Tina didn't know that, but I did, so when I first met her I said, 'I know your grandma!' She was really shocked, but straight away I felt like I was with family. It was really easy to settle in there."
Are you similar to Chantelle in real life?
"At first, I thought we were quite similar, but the more I learn about Chantelle, the more I realise that she's much nicer than I am! She's got what maybe I used to have - which is being naïve to the bad side of life. She's a few years younger than I am and she's been quite sheltered.
"I've been doing this career for ten years now, so I've learned a lot and maybe grown up quicker than I would have done otherwise. But Chantelle is particularly naïve, very optimistic and very positive. I'm a very positive person too, but Chantelle thinks the sky is the limit."
What kind of a reaction do you get from Holby fans?
"Everyone is very, very lovely to me. I think people want to give Chantelle a hug, so I get plenty of hugs from people that enjoy the show! Generally I just get well wishes, because people want Chantelle to do well."
Is it nice to have some newcomers on set at the moment?
"Oh, it's lovely. Chizzy [Akudolu] and Michael [Thomson] are our newest cast members, and they're so full of life. They are lovely to be around and although I don't work with them all that much, they brighten up the make-up room, that's for sure!"
We've also seen a few cast members leaving recently, so are you missing them?
"You work so closely with people, so you can't help but miss them. In particular, myself and Jimmy [Akingbola] miss Adam [Astill], who played Dan. We miss everyone, but unfortunately that's the nature of it - the show moves on and we get new characters in. But I think everyone who has worked on the show leaves a mark on it."
Who are your best friends on set?
"I see a lot of Tina and Jimmy. Jimmy hosts some great parties in Soho, so we often have cast get-togethers. At work, I spend a lot of time with Hugh Quarshie, who plays Ric. I have a lot of time for Hugh - he's a very inspirational person and I learn a lot from him."
You also appeared on Holby as a guest artist a few years back, so do you have many memories of that?
"Yeah, it comes back to me! I only realised about a month ago that it was on the same ward that I now work on. In a few weeks, I'm actually going to work with the same director who directed me four years ago. I haven't seen him since I started, so it should be fun to reminisce with him."
Are you hoping to stick around on Holby City for a while, or would you like to try other roles?
"Well, I'm only 24 so there will come a point where I want to try other roles, but for the time being I love playing Chantelle. I'm very happy there at the moment!"
> Read our spoiler for the next 'Holby City' episode
> Read more 'Holby City' news and spoilers
Holby City airs tomorrow (July 3) at 8pm on BBC One.