The story plays out 4 different characters, which are all linked together by their own actions, through out this movie. The audience wont get to know the characters in depth, but only a sense of their personalities that will visually be displayed through the narrative and how their actions link them all together in the end.
Sam steals a phone which creates a ripple effect. This ripple effect intertwines other people's stories and results in ultimate karma. After stealing the phone, Sam goes to a club and see's a potential victim. He spikes her drink.
As he tries to move in on Emma, who can clearly feel the affects of the Rohypnol, the bar man recognises him and creates a scene trying to get Sam to move on. Very confused, this scares Emma and she runs out of the club and in to the nearest taxi.
The taxi driver tries to hassle Emma for more money than the respective journey is worth. Meanwhile, Sam exits the club an is trying to make the stolen phone work. With neither the taxi driver, nor Sam paying attention, the car knocks Sam down.