The only thing worse than a confusing movie is if it's so boring that you can't be bothered to try and figure it out.
So probably best to start with the flashbacks. They first met about 5 years earlier in Dubai, when Ray was seduced by Claire, and then drugged for 17hours as she stole plans from his hotel room.
Later, they met in Italy and ended up in bed together where they started to make plans. Their initial conversation they liked so much, that you hear it again ... and again ... and again in different situations. It doesn't get any better after the first time.
Ray wants to work in a frozen pizza advertising firm who are about to release a Hawaiian that he claims is the first one ever to be distributed in frozen form. Dude, that's been out for about 20years. Honestly, why is that even in the movie? Claire convinces him that she has found a sweeter deal, and so he gets in on the rival global firm.
So, the end. One of Claire's colleagues has been found trying to steal the secret formula from the firm HQ. While the security staff search the building, Claire blindfolds him and runs off with the formula looking for a way to send it to the rival firm. They find a photocopier that sends a digital signal, and Ray keeps a copy as it is sent through.
Claire meets the rival team, and accuses Ray of keeping an extra copy. They search him and find it. You'd think that he's pretty much dead at this point - or at least beaten up for all that.
But no, he meets Claire at an airport a little later without a scratch. They both share their true feelings - Claire has a picture of the formula on her mobile, and Ray managed to somehow keep a 3rd copy, which makes no sense. They go to Switzerland together to meet an interested buyer and plan to sell it for $40million.
At the Swiss hotel, a team of scientists test the formula, but find it is only for a simple lotion and pull out of the deal. Meanwhile Paul Giamatti's character gives a major speech to the shareholders (even though it is a crowd of thousands, so some must surely have shares of only a few dollars and are just along for the ride). He reveals that they have found the cure for baldness, to be sold as shampoo. The crowd goes wild, and of course with the false promise he has effectively killed his business empire.
The rival CEO, Tully, meets with his covert team, involving people from both sides, and it is revealed that they played Ray and Claire all along.
Ray and Claire sit alone in the Swiss hotel foyer, and are served a bottle of champagne, coutesy of Tully.