This takes place during Aftershock Pt. 1, after Terra's attack that she believes killed the Titans. I tie it into the ending dialogue from that episode. Also, just wanted to elaborate on something Beast Boy said that I always think is kind of odde, and have a little BB/Robin friendship moment because there are so few positive interactions between them in the show.
Terra's last attack on the Titans devastated them. They were scattered around town, injured, and unaware of the condition of their teammates. It took three days for the five to locate each other, address the most severe injuries, and carefully gather intel they would need when they were finally ready to confront Terra again.
Everyone needed rest and they decided to spend one more night in the underground cavern beneath the tower. No one was happy about being in hiding, but after the trauma of thinking their friends died by the hands of their former teammate, the short time to recover was necessary. Mostly they just needed that time to be together.
Raven was gathering a few supplies, being able to quickly teleport in and out of the tower to avoid notice, and Cyborg was trying to create better lighting so Starfire wouldn't need to keep holding up a starbolt and he wouldn't waste power on his shoulder light.
Robin was trying to focus on a plan, but his attention kept shifting to the boy sitting nearby.
Since he was found Beast Boy had been quiet and withdrawn. This was unusual for him and concerning for the Titan's leader. While they were all hurt by Terra's betrayal, Beast Boy and Terra had gotten close. Robin knew his youngest friend felt things very strongly and was disturbed by the blank expression on his face.
Robin shifted to sit closer. "You okay?"
Beast Boy shrugged. "As okay as I can be after getting thrown down a hole." Beast Boy gave him a weak smile. Even in the dim light Robin could see that it didn't reach his eyes.
A few moments passed in silence before Robin spoke again. "I tried to talk to her. Tried to give her another chance, like I promised I would. I really did try."
"Thank you," Beast Boy mumbled. "I shouldn't have said that."
"What?" Robin asked, thinking he heard wrong.
"I shouldn't have said that. About you working for Slade." Beast Boy sighed and looked away. "That was different. You didn't choose that. She did. I'm sorry."
Robin laid a hand on Beast Boy's shoulder. "It's fine. I understand. And you all gave me a chance before you knew that it wasn't my choice. It meant a lot knowing that you were trying to find reasons, find an explanation. That you all tried to reach me. We extended that same grace to Terra, and…"
Here Robin paused. All five Titans were back in the cavern now, and he noticed that by now they were all listening to him. Unfortunately there was no comfort to give here. All he could do, for Beast Boy and the rest of the team, was to be the leader. It was time to address the reason they were all there. "And she rejected it. We know it's her. We know she's doing this willingly. There's nothing else we can do."
He felt a slight tremble from the boy next to him and then Beast Boy was looking at him again, more serious than he'd ever seen him. "I was holding back before. I won't now."
The air was tense. Everyone in the room had the same thought and with hurt and anger they spoke it into the cavern.
"No more chances."
"No more trust."
"And no more mercy."
"She's just another criminal."
"And we're going to stop her, no matter what it takes."