Unfortunately, the trade-in event gets lit up by The Mayor himself (where the local cops prove completely useless), and Sin ( Bex Taylor-Klaus) gets shot in the process. At the same time, Arrow and his team track the weapon supply to a local military base thanks to one of Diggle's informants (and possible love interest?). To move the plot along, Oliver sponsors a "Cash 4 Guns" trade event to get the weapons out of the Glades. This bit comes into play later on, as well. Oliver then reveals to Diggle and Felicity that he saw Sara a year after the sinking of the Gambit. In a big reveal (that was unfortunately spoiled for myself and many others by IMDb's cast listing), Black Canary is in fact Sara Lance ( Caity Lotz), the sister of Laurel who accompanied Oliver on his ill-fated voyage on the Gambit, and was presumed lost at sea. More interesting than The Mayor is Black Canary who, it turns out, is following Laurel, allowing Arrow to track her down and interrogate her. What happens to him by episode's end, however, is worth noting. The Mayor isn't very interesting as he amounts to nothing more than a jumped-up thug. This cold open establishes everything we need to know about this particular episode's plot right out of the gates, including the new enemy of the week, The Mayor ( Clé Bennett). Laurel ( Katie Cassidy) attends with Sebastian Blood ( Kevin Alejandro). Arrow and Diggle ( David Ramsey) discuss the stolen weapons in the gang's possession. During a soiree at the Queen family mansion, Arrow ( Stephen Amell) cleans up some gun-toting criminals in the Glade while Felicity ( Emily Bett Rickards) stalls Oliver's guests, including hostile CEO Isabel Rochev ( Summer Glau).