What mistake did Oliver and Diggle make?
That was revealed on Arrow Season 6 Episode 17 when the two heroes realized the big blunder was going to have horrifying ripples through Star City.
Meanwhile, Black Siren continued to try and get closer to completing her mission, but did someone stop her before it was too late?
Also, Curtis revealed a shocking truth to his new boyfriend, but did it signal the relationship being a temporary affair?
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Paul Dailly is the Associate Editor for TV Fanatic. Follow him on Twitter.