When a distracted Maggie calls off the ceremony at the last minute, Grantly (Philip Martin Brown) is left stunned by her sudden change of heart. However, following some detective work from Scout, it soon becomes clear that Maggie's decision has been influenced by a face from her past.
As Grantly vows to find out what is going on, he discovers that Maggie is being blackmailed by her ex-partner Trevor, who she never divorced…
Digital Spy recently chatted to Melanie Hill, who plays Maggie, to hear more about the storyline and life at Waterloo Road.
Have you settled in well at Waterloo Road's new Scottish home?
"Yes, really well! It took a while at first, because the show was so well-established in Rochdale and it was a great place to work. I live in London, so the move was quite a long way and a lot to commit to, but it's been nine months now and I think within a few weeks we all found our feet.
"They've done such an amazing job with the move, and the people here in Scotland have just been so welcoming, so I feel like I've slotted in."
The schoolhouse has provided Maggie with a new responsibility on screen in this series. Have you enjoyed those chaotic scenes with the kids?
"I have - a lot! It's nice to get out of the school for a while, and I think it shows a different side to all of the characters when we see what they're like before school and after school.
"Also, with Maggie not being a teacher, she's not confined to the behaviour that a teacher would have. That means she can overstep boundaries and push things a bit further with the kids - she can let them get away with a bit more than the teachers would do! Maggie has been able to form some nice relationships with the kids in the show, so I've enjoyed that side of it as well."
Why do you think Maggie and Grantly are such a good match?
"I think the two of them met at a time in their lives when they were quite lonely people. Grantly was having a trauma with his wife at the time and that was awful, but Maggie got close to him and she was there for him.
"When you get to our age, it's more of a companionship rather than instant love and passion. What's happened is that they've formed a massive friendship, and then a deep love has come from that. Also, I think they've both got a massive sense of humour. Maggie softens Grantly a lot, so they're good foils for each other."
What can you tell us about the wedding episode?
"I was really looking forward to filming this episode and seeing how it would all pan out. But as soon as the episode starts, Maggie calls the wedding off and there's a massive problem. It becomes clear that she's done this because someone is blackmailing her, so then it's a case of whether the wedding will go ahead and who's responsible.
"It's nice that it doesn't all just run smoothly - obviously in typical Waterloo Road fashion there's some disaster along the way! But I think Grantly and Maggie are good for each other. In episodes to come I'm sure they'll have their ups and downs, but they do definitely have a future together."
As the episode goes on, we see that Maggie's estranged husband Trevor is the one who's blackmailing her. Does the episode delve into Maggie's past?
"You find out the story between those two, but we don't actually have any scenes together! Funnily enough, Bill Fellows is playing my husband and I've played his wife before in a film called United. Again in that film, I never had a scene with him - so this will be my second screen project where we're husband and wife without interacting with each other! Hopefully there'll be a third time lucky one day!
"It's just the way everything worked out with the storyline - it's down to Grantly to sort everything out. He needs to deal with Trevor and save the day. That's good for his character, because it's another side that Philip is able to show to Grantly. He's trying to rescue Maggie, which is lovely and sweet."
What's the overall feel of the episode?
"Well, the fact that we're older and obviously the Waterloo Road fanbase is quite young did worry me, so I didn't want it to be too schmaltzy or embarrassing. But I was assured that the story would have humour and the audience would go with it.
"Grantly is one of the fans' favourite characters and there's a lot of affection for him, so I hope we've approached it in the right way. I've had some good feedback so hopefully we have."
Did you help to choose Maggie's wedding dress?
"It was chosen for me - to be honest, I was a bit worried because I'm not a spring chicken anymore and I don't wear dresses as a rule. But they did a great job, and the one that we used was the first dress that I tried on. It ended up being fun and I really enjoyed the filming days for this. It was nice to be in an actual party atmosphere - everything was fun and not too serious."
What can you tell us about what you've been filming recently?
"We're just starting the final ten episodes of series eight, which won't be on screen until next year. I can say that Grantly and Maggie have got a lot of lovely stuff coming up. There's lots of adventures, some ups and downs, but it's so far, so good with them together and long may it last!"
How does Waterloo Road compare to your previous work?
"I've done a lot of ensemble pieces, so that's similar, but I've not really done many projects where half the cast are very young. There's lots of kids in Waterloo Road, and that's been great - it's different for me working with the youngsters.
"Also, the fact that I'm in a long-running project means that I have time to form stronger relationships. I'm used to doing a lot of one-off dramas as well, where you've got to meet people, spend five weeks and then move on. So you get spoiled in a way - I'm enjoying staying in one place."
Do you find yourself taking the younger cast members under your wing?
"I do, to be honest. I think I'm quite typecast because Maggie's quite a mother hen, and I do feel responsible for them. Not so much the boys, but the girls - I've got close to them all. They're away from home and it's important they know that the older cast members are there for them if they need anything. We are quite a tight team now, so it is nice."
Is there anyone from the current younger cast who you'd tip to go far?
"There's a lot of them, but I think Shane O'Meara who plays Connor is very good - him and Kirstie Steele (Imogen) are ones to watch. They're all good, but to me they've stood out."
Have you suddenly found yourself with a younger fanbase thanks to Waterloo Road?
"I have - people often remember me from Bread, but the youngsters are too young for all of that and they've never seen it. So now I'm getting young people coming up, which is nice and refreshing. When a young kid of 12 comes up and says, 'Can I have your autograph?' it's quite a surprise! And of course they adore Philip, so every time I'm sat with him he gets mobbed."
Do you have fond memories of your own school years?
"I do. I grew up in Sunderland, and I was a bit of a swot at school. I was quite boring, so I've got no juicy stories or anything! I remember doing a lot of sports and having a good time. I started doing drama at sixth form and that's how it all started. I owe my school a lot, especially the drama teacher."
Are you sticking around in Waterloo Road for the long haul?
"Yeah, well I hope so! You never know, because it depends on where they want to take your character and what their plans are - there's so many different factors. But as far as I'm concerned, I definitely am because of all the reasons I've said. I'm really enjoying my time here."
> Read our full spoiler for the next episode of 'Waterloo Road'
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Waterloo Road airs Thursdays at 8pm on BBC One.