'You' Season 4 Part 1 left a big clue about what's going to happen next

A new season of Netflix's You is here, and Joe (Penn Badgley) has found himself right in the middle of a mystery. Unfortunately for all of us, this season is split into two parts, so we have a month before Part 2 drops on Netflix for more answers. But, in happier news, there's a giant clue hidden in these first five episodes...