i got two ideas for the plot (sorry if it's kinda crappy)
Basically, Gerard and Frank are quite far into their relationship but an old friend returns (you decide) and wants to ruin the relationship and bring Gee, Ben, Nate and Rose to justice
or
Some person (you decide) who is related to one of the victims kidnaps Frank and threatens Gerard to turn himself in along with Ben, Nate and Rose or Frank gets killed