When cash-strapped writer Tom Cartwright is offered the highly lucrative task of ghosting the autobiography of a glamorous young soap star, he and his girlfriend Sara are thrilled. Sara is a great fan of Georgina Nye's, and Tom will finally be able to afford some new carpets for their flat.

But things soon go awry when Tom finds himself drawn to Georgina by forces outside his control (even though they are inside his own body). Does his five-year relationship with Sara stand a chance in the face of this explosion of chemistry? Are he and Georgina bound by emotional attraction? Or is it simply vasopressin being released by his pituitary gland? And is this love? Or just the hormone oxytocin? Most importantly of all - is there a difference?