It is the year 1715, and Thomas True has arrived on old London Bridge with a dangerous secret. One night, lost amongst the squalor of London's hidden back streets, he finds himself drawn into the outrageous underworld of the molly houses. Meanwhile, carpenter Gabriel Griffin struggles to hide his double life as Lotty, the mollies' silent guard. When the queen of all 'he-harlots', Mother Clap, confides in him about a deadly threat, he realises his friends are facing imminent execution. To the horror of all mollies, there is a rat amongst them, betraying their secrets to a pair of murderous Justices, hell-bent on punishing sinners with the noose. Can Gabriel unmask the traitor before it's too late? Can he save hapless Thomas from peril, and their own impossible love?