We are in the home stretch and CBS has been running this ad for the third to last episode of season three. [SPOILERS]
Greer runs his beta test of Samaritan searching for Harold. Instead he finds Grace Hendricks. Holy shit.
From the short cuts of the trailer we see that Greer might have and is even speaking to Grace about the man she loved Harold Wren. What's awesome is that Harold has his identity so wrapped up in lies that not even Samaritan can find him right away. But the most interesting part is that after the Machine gave them a number to kill to prevent Samaritan from coming online, Harold left the gang to places unknown. He doesn't kill he saves, until you fuck with Grace. He actually says "If they harm her in anyway, kill them all." Kill them all has to be one of my favorite phrases to be uttered, and I have been noticing its being used more in recent years.
Maybe this is Harold's moment of crossing over to the darker aspects of the grey morality he subscribes to, because in the face of Decima's machine the gang is going to have to get ruthless to survive.