After returning home from a somewhat dull business party, married couple Joanna (Keira Knightley) and Michael (Sam Worthington) get into a fight. There was a woman at this party, you see, and Joanna suspects that she and Michael are having an affair. Since it was his business party, and because she works at the same company with him and he never said anything about her, clearly this means he has something to hide.

The fight is eventually quelled and the two get back on good terms. Michael is leaving for Philadelphia in the morning, though, and this woman, Laura (Eva Mendes), will be joining him. Joanna stays at home, as she’s a writer, having put out one book and now working as a freelancer writing fashion magazine articles. She says at one point that putting out one-hundred words is difficult enough. I didn’t detect sarcasm in her voice, but maybe it was there. I certainly hope so. The couple’s apartment looks too expensive for one salary to maintain.

Anyway, while husband is in Philly, wife is going to get a visit from an old friend named Alex (Guillaume Canet), a man who has such an endearing smile. It’s no wonder that Joanna loves him and hasn’t told her husband about him. Oh, but they haven’t seen each other for over two years now, and have even stopped emailing. Despite this, Joanna lights up like a Christmas tree when he appears as she’s getting a cup of coffee. They’re going to spend the rest of the movie together, just like Michael and Laura are going to get nice and close.

At this point, you’re probably wondering two things. (1) Have the two married individuals cheated on one another in the past, and (2), will they during the course of the film? The first question I’ll answer with a “no,” although you’d have to define “cheating” better first. the second question I’ll leave for you to find out, as it’s only kind of what the main focus of the film is and I’d be ruining the only mystery that Last Night has if I were to give that away right now.

Whether or not the characters will cheat on each other — or what cheating really means — becomes the sole focus of the picture. There’s nothing else going on, and it seems the night the couple spends away from one another is dedicated only to find out whether they can muster up the courage to do something they both clearly want to. A dog also finds a way to get involved, providing the film’s only comedic relief. One character remarks that Joanna is a funny person, but she certainly didn’t come across that way to me, nor did anyone else. They had to remain focused on making the tough decision of whether or not to remain faithful.

With such a simple story, you need strong characters and performances to carry much of the film. You know pretty soon into watching that you’re not actually going to get a resolution — if you’re even going to get one — until near the end. The events leading up to this conclusion are mostly filler, so having deep characters and strong actors is very important to the success of the film. We get a mixed bag here.

I did think that the characters were deep enough, and for the most part, they’re performed well. You generally understand the way that the characters in the Joanna/Alex storyline feel, and their points end up being the highlights. You team two pretty good actors together and you’ll have something watchable. On the other hand, the Michael/Laura story falls flat for most of the time. Most of the time we spend with them is used to talk about past and current relationships, rarely changing location and never actually becoming meaningful. There was no chemistry between them, and while I thought Worthington was decent, Mendes continues to show that drama isn’t her forte.

With Laura and Michael not having any real chemistry, while also not doing anything of value, their story kind of falls apart in the middle and never picks itself back up. Granted, when the time came to make the decision, I did want to see Michael make the right one — and that isn’t as clear-cut as you’d first think — but that’s more due to the Joanna/Alex story and what I saw there instead of what happened, or didn’t happen, between Michael and Laura. Half the film doesn’t work, while the other half only sometimes succeeds.

The only other thing worth mention is Last Night‘s ending, which took courage and left us wanting more. Yes, you’ll get your answer to question #2 answered, but you won’t really get any more than that, especially what it means for the individuals involved. If this was an action film, we’d be chanting “sequel.” I don’t think there will be a sequel to this film, nor should there be. We leave on the perfect note, even if it doesn’t answer everything you want to know.

Last Night is ultimately a film that only works in pieces and rarely, if ever, comes together as a satisfying experience. It contains two mostly separate stories about two souls tempted to cheat on their partner, but only one of these stories works and only then because of the actors involved. With that said, there’s more depth and reasoning that goes into the decision making process, and I have to admit that I was hoping the characters would make the right choice. What that is, I’ll leave you to find out. This isn’t a film put together well, but it still works to a surprisingly large degree considering how much of it I didn’t like.