SPOILERS AHEAD! BE WARNED!The costermongers of Spite sell chestnut-mushrooms, blind cave herring, smoked bat... and secrets. The Steely-Eyed Costermonger needs you to take a secret to a colleague five streets away. Time is of the essence.
Note: Since you need at least 5 Shadowy to be a courier, and since 5 Shadowy is enough to always succeed in this challange, failure is now de-facto impossible, unless you switch to Shadowy reducing gear when you're at the A courier job storylet.