In the song, Olly is talking about a past relationship which he was reminded of when he bumped into 'Irene'. The basic message of the song is that Olly's ex-girlfriend will be thinking of Olly when she does certain things, like picking up pebbles of the beach or listening to Bob Marley.
I really enjoy the reggae fusion in the song, makes you just want to get up and dance a long. (Or is that just me?) The lyrics are extremely catchy, and you will find yourself singing them in the shower. I'm very glad the duet with Professor Green fell through, as it would have made the song a complete mess. So it's a thumbs up from me!