Julia, a no-nonsense neuroscientist, whose research into the biochemistry of the female brain is illustrated by three couples: newlyweds Zoe and Greg, whose career troubles seep into their relationship; Lisa and Steven, who are looking to spice up their stuck-in-a-rut marriage; and Lexi who can't help trying to change her boyfriend Adam. Meanwhile, the straight-laced Julia's own synapses start to fire when a handsome new subject joins her study.