Looks like you need to have already talk to him there at least once, have met your full team at Slate's detective office, and met Stryker with Boss' night work events.
Talked to Nocturnal before.
and did stryker in Boss Night work.
...but i dont think i have that "full Team at slates office" thing...is Slates office an actual added place or an event that is triggered? if it is triggered, who do i need to talk to? Slate or someone else?
i can meet slate in the neighborhood and in the winners circle bar but in both he has the same repeating events.
overall i seem to be missing the "new detectives in town" event. if its that.