WARNING! The following article gas SPOILERS for the Arrow Episode "Life Sentence"
"Life Sentence", the final episode of Arrow's sixth season, ended with Green Arrow scoring a Pyrrhic victory over crime boss Ricardo Diaz. The Emerald Archer was able to save his city, exposed the government officials on Diaz's payroll and protected the rest of Star City's vigilantes from prosecution under the city's new anti-vigilante law.
Unfortunately, accomplishing all this required that Green Arrow expose his secret identity as former mayor Oliver Queen and turn himself in to the FBI to face various federal charges, resulting in the titular "Life Sentence." What is worse, Green Arrow's sacrifice ultimately did little to thwart Diaz's ultimate goals. True, Diaz lost the army he built out of Star City's corrupt police department and all the allies he had in the city government. Yet Diaz still accomplished his three biggest goals - taking over the criminal organization known as The Quadrant, seeing Oliver Queen removed from office as Mayor of Star City and putting Oliver Queen behind bars after revealing him to be The Green Arrow.
To top it all off, Diaz is still at large to enjoy the fruits of his success. And he owes it all to one person - a former ally turned enemy, whose heel-face turn (to use the professional wrestling term) may have been a feint within a ruse within a hoax - Black Siren.
On the surface, this may seem unlikely given the events of recent episodes. Black Siren tried to kill Diaz at the end of "Docket No. 11-19-41-73", having grown fearful that Diaz would hurt Quentin Lance - the one person who had ever been nice to her without any ulterior motive. Yet "Life Sentence" revealed that Black Siren was still alive, despite Diaz being characterized as a deranged lunatic, who has killed treacherous and incompetent underlings for far less than trying to kill him.
At first it seemed that Diaz was only keeping Black Siren alive as a bargaining chip to manipulate Quentin Lance. Yet once he had both Black Siren and Lance in his clutches, he elected to shoot Lance rather than follow through on his threat to kill Black Siren, in a bid to make Lance do what he wanted. This was a decidedly illogical action since Diaz needed Lance alive and had no reason to keep Black Siren alive - unless she was still working with him and had only pretended to betray him earlier.
It was at this point that Green Arrow and his allies arrived and Diaz made a run for it. Green Arrow gave chase and the two fought on the rooftop of Diaz's hideout, as Diaz was trying to summon a getaway helicopter. Green Arrow won the battle handily and had Diaz dazed. Suddenly, Black Siren appeared and let loose one of her trademark sonic screams, apparently blasting Diaz off of the roof and into the waters of the nearby bay.
Black Siren wrote this off as her needing to "end it", but Green Arrow said there was no way that fall could possibly have killed Diaz. The FBI disagreed, saying there was no way Diaz should have been able to have survived the fall and managed to get away. And yet, as the montage at the end of the episode revealed, Diaz did get away, despite not having the metahuman toughness required to survive a point-blank sonic scream, a multi-story fall and a hard landing into freezing waters.
This doesn't make any sense, unless one considers "Next of Kin" - an episode from earlier in Season 6, where Black Canary was able to use her Canary Cry to cushion and direct the landing of a free-falling John Diggle. Black Siren has been previously depicted as having a similar level of control and power as Black Canary, so the chances of her being able to manipulate Diaz's fall so that he landed safely are high indeed.
So is Black Siren still working with Ricardo Diaz? It would certainly explain a lot. The only certainty is that it will be a tense few months for Arrow-heads everywhere as the wait for Season 7 begins.