Ben and Lily couldn't be more different. He's flash, brash Bermondsey boy - an advertising man - and she's a quiet, bookish English teacher from genteel Beckenham. In fact, the only thing they seem to have in common is their mutual dislike of one another - that and their participation as inmates in a clinical trial. Then everything changes. Suddenly, they're hopelessly, happily in love and blissfully unaware of the strangeness of their new-found feelings. But when Ben begins to wonder about the possible side effects of Pherexosol, the experimental drug they're both on, and makes the decision to stop taking the pills, their relationship shifts yet again. Only this time, everything's just a little more complicated and they both have far too much to lose.