Liam Neeson is Bryan, a former government agent of some description. He has a particular skill set, that of a highly trained killer. His daughter, while holidaying in Paris is kidnapped by human traffickers specialising in sex slaves, so Bryan sets out to find his daughter again.
There's more to the plot, but you won't care about it. In fact, in several places it threatens to spoil all of the awesome, brutal violence that is to follow. The opening act, establishing the characters, is far too long and devoid of fight scenes. The emotional scenes don't quiet cut the mustard, and Famke Jannsen is just kind of annoying (never thought I'd see myself saying that).
Thankfully, all of this rubbish more or less passes, and what is left is a very good modern, mindless action flick. Think of it as Jason Bourne meets Steven Segal and it starts to make sense. The action is hugely inspired by Bourne - fast-moving, gritty, big body count - but the genre is all Segal - the best at what he does ex-military/government agent risks all to rescue a family member. It may not sound too great like that, but try watching Under Siege 2 without smiling at how stupid and enjoyable all of this action is.
It's a B-action movie for the 21st century - devoid of any deep meaning, but bags of fun to watch. B.