Buffy received a phone call from Angel. Having learned about her resurrection, he wished to speak with her, so Buffy left to meet up with him. This meeting was the subject of Jane Espenson's comic Reunion.
The periscope in Warren's basement has Russian lettering on it. When read phonetically, it says "geek". This however might be just a coincidence, since it's what comes up if one changes their keyboard layout to Russian and types "USSR".
The Trio was originally supposed to include Tucker Wells, another Sunnydale High student who had previously caused trouble for Buffy and who was originally meant to be the leader. Since Brad Kane was unavailable, the character of Andrew Wells was created instead and Warren was made the leader of the trio instead.
After receiving the phone call from Angel, Buffy says they won't meet in Sunnydale or in L.A. "Somewhere in the middle," was a nod for the fans, since the WB would no longer allow crossovers after they cancelled BtVS and it moved to UPN for its final two seasons. WB would later relent, allowing David Boreanaz to guest star in the last two episodes of season 7, for the trade-off that Alyson Hannigan would guest star in season 4 of Angel, during the Angelus returns arc.
This is the first appearance of The Trio. Adam Busch has appeared as Warren Mears and Danny Strong has appeared as Jonathan Levinson in previous episodes but this is the first appearance of Tom Lenk as Andrew Wells.