After the slumber party at Rarity's, the humane 5 are shocked to discover that the pictures that were taken during the slumber party have been posted on Anon-A-Miss's page for the whole school to see. pictures that were taken using Sunset's phone.
Naturally the girls assumed that Sunset was Anon-A-Miss and when she didn't show up at School it further proved her guilt. But when they visited her apartment using the spare key Sunset gave Rainbow Dash in case of an emergency, they discover a very ill Sunset resting on her bed.
Pushing their anger aside to aid their sick friend the girls soon discover that Sunset is not Anon-A-Miss as whoever it is made a post while they were watching Sunset.
Now as they figure out who Anon-A-Miss could be, Sunset's fever continues to get worse and when her body starts flashing red, they realize that whatever Sunset has is beyond their world's ability to treat.