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There are a lot of really good things about Bridget Jones’s Baby, the fun and surprisingly thoughtful third film in the Bridget Jones trilogy. But more than anyone else involved, we ought to be grateful to Colin Firth, who plays leading man Mark Darcy. Without Colin Firth, Bridget Jones’s Baby might never have existed, and if it had, it would have almost certainly been without its best feature – a successful cinematic portrayal of the ups and downs that make up any relationship.

Before we can get into the details of that, though, a bit of background is in order. Bridget Jones’s Baby is the third film featuring Bridget Jones (Renee Zellweger) and her entanglements with on again/off again love Mr. Mark Darcy. The first two – Bridget Jones’s Diary (2001) and Bridget Jones: The Edge of Reason (2004) are based on books. The third book in the series, Bridget Jones: Mad About the Boy came out in 2013, only there was a small change to the formula: Mark Darcy had died. There was no way Hollywood was going to greenlight a big screen adventure for Bridget without her much-loved beau and sparring partner, so they decided to create an entirely different story about an accidental pregnancy. The paternity is uncertain – is the pregnancy the result of a spontaneous drunken tryst with Jack (Patrick Dempsey) at a music festival? Or a nostalgia-driven backslide with Mark a week later? Only 2 hours in the theater will tell.

The trio credited with the screenplay is an unconventional set, consisting of Helen Fielding, who wrote the Bridget Jones novels; Dan Mazer, who is best known for his work on Borat and Da Ali G Show; and actress and occasional writer Emma Thompson. Thompson has done a few screenplays since her 1995 adaptation of Sense and Sensibility, and we should insist she do even more writing if she drafted even a third of her own lines in Bridget Jones’s Baby, in which she plays an acerbic OB/GYN with a heart of …well, with a heart of some kind. The script is not perfect – the writers seem to have drawn their conception of a successful professional adult woman from some combination of Aaron Sorkin shows and I Love Lucy – but it’s entertaining and fun most of the time, and believably earnest when it needs to be. The goofy physical humor is balanced well with sharp jokes that make people in the movie laugh as much as the audience.

The supporting cast in the film is as much fun as it was 15 years ago, from Gemma Jones and Patrick Broadbent as Bridget’s parents, to Sally Phillips, Shirley Henderson, and Agni Scott as her friends. New addition Patrick Dempsey is no Hugh Grant, but Dempsey is essentially a professional charming person, and he’s a good fit for this kind of movie. As always, though, it’s really Zellweger and Firth whose chemistry is most compelling – not because it’s explosive, but because it’s fickle, which is arguably even harder to play. You can go from believing the Bridget and Mark are meant to be together in one scene, to wondering in the next if perhaps they should try to avoid being in the same room. No relationship between these two will ever be simple, but the fact that they encounter real-life relationship problems and need more than just love to make it work feels more real than if the series had ended with the usual “happily ever after” ending.

And this is why we owe a debt of gratitude to Colin Firth. If Firth hadn’t been so beloved to movie audiences as Mark Darcy since back in 2001 (or maybe even as a different Mr. Darcy way back in 1995), studio executives might not have insisted on a complete departure from the third book, thus keeping Darcy in the mix for the third movie. I wrote earlier this year about why sequels are rarely seen in romance: it’s hard to create believable new conflict without undoing the happy ending that first satisfied audiences. But if a movie can pull it off, it can be a better representation of what life is really like. We now have the chance to see this couple slogging through the reality of trying to keep a romantic relationship going – sometimes it works, but sometimes it doesn’t.

Also, we wouldn’t have had the chance to be reminded of Bridget’s best and most aspirational trait – she takes responsibility for her own happiness. She feels a bit abandoned by her friends with kids, so she goes away for a weekend with her single friend. Her romantic life isn’t what she’d imagined, so she focuses on her job (only sort of successfully, but it’s the effort that counts). Maybe most importantly, we see a flashback from before the film indicating that her relationship with Mark wasn’t working. So she walked away.

Of course, the beginning of the movie brings a new chance for Bridget and Mark to end up together. Or maybe it will be Bridget and Jack! Either way, this isn’t a movie aimed at showing us that single women can be happy and successful raising children on their own. Someday it might be nice to get that movie – or even the version that doesn’t include children – but that’s not Bridget Jones, and that’s okay. The fact that Bridget wants to be married and have kids doesn’t make her bad or pathetic, nor does it make her noble or mature. She’s just a relatable character who is well-loved and who pursues happiness in whatever form it takes on any given day. Bridget Jones’s Baby gives her a funny, sweet, charming film in which to do it.