Four years ago, during probably one of the Riddler's earliest trips to Arkham, an unseen guard is quite the dick to him, roughly manhandling him after they discover playing cards in Riddler's cell. Fast forward a couple of years, and Riddler has started a flash mob of protestors outside of Wayne Enterprises, angry about some scandal involving SEC filings. Riddler, without his mask, cane or hat, uses the chaos to make his way into the building, with help of a forged access card that gives him access to many of the computer systems within the Wayne Enterprises building.
As Riddler ascends (now dawning his full costume) the building, he is spotted by the team monitoring the cameras in the security room, who then alert the rest of the security in the building. But this hardly manages to get in the Riddler's way, as he distracts the dumber guards with riddles and eventually uses whatever gadgets he has to get past them.
Riddler eventually uses the Junior VP of Finance to access a more locked off area of the building, and doesn't take kindly to her fighting back (Riddler doesn't like to be touched) and once that ordeal is over, he makes it back to what seems to be his old office from Zero Year. It's here where the chief of security finds him, and it turns out that he was the guard who we saw rough Riddler up in the flashback. The two start to fight, but Riddler eventually asks "I'm sorry that I woke today, because i've lost my right. I'll sit here in the corner now, and mumble at my plight. What am I?" Answer: The guard himself. "Lost my right?" Well, that's his right arm, the arm he used to touch Riddler, and it gets blown off by one of Riddler's numerous gadgets.
With his main goal of the night accomplished, Riddler finally ascends to the roof, looking over a Batmanless Gotham, and picks back up the game of solitare that had been taken from him four years ago.