ELI5: Explain Like I'm 5

lost the plot

Lost the plot means that you no longer understand what's happening in a story or situation. It's like when a movie or TV show gets really confusing and you can't remember how all the characters are related, or why the main character is doing something. It can also happen in everyday life, when you feel like you're not really sure what's going on or why people are doing the things they do.