After the poorly-received trilogy of character-driven episodes focused on Sarah, the writers return to the larger canvas with this episode. In essence, this is the beginning of the final leg of the season, as events begin to spiral out of control.
Riley's suicide attempt was just the beginning of trouble for the Connors, because it happened in the Connor home and after Riley's freakout with her foster family. Those chickens come home to roost in this episode, and they coincide with an interesting new malfunction for Cameron. It looks to be quite a rough time. Riley's death is going to bring external and internal pressures that have been lingering in the background for quite some time.
Externally, the Child Services investigator seems like a minor threat, but anything that brings unwanted attention to the Connors is a disruption that cannot be tolerated. Riley's death is only going to throw more suspicion on them, especially given the coincidental timing. Considering how many times Sarah has wanted to move on and escape potential detection, this is just another such trigger. Internally, the Connors have every reason to believe that Cameron was the one who killed her. John, particularly, has reason to suspect Cameron, given her admission that something unexplained is happening to her.
Jesse's plan was rather brutal in its simplicity, and while it didn't quite work out in terms of the details, the end result works in her favor. Cameron is the most likely suspect under most circumstances, and Derek has never told the Connors about Jesse. In fact, the only person who might have a reason to suspect Jesse is Derek, and right now, he has no compelling evidence to connect Riley's death to her. (Her absence from Derek's mission, of course, is the likely starting point for his inevitable investigation.)
The pacing in this episode was still a bit slow and methodical, much like the previous episodes, but the momentum of the plot was more than enough to overcome that slight drawback. The pieces are moving into position for one hell of a conflict to round out the season, and Riley's death is likely to be only the first among many.