The Youtubers meet Amber Liu
Jack, Felix, Marzia, Ken & Mary visit Mark in L.A as a surprise. It's Marks birthday so they wanted to do something special. They already spoke to his family about it and they all wanted to take him out on a fun day but when Mark is almost hit by a car, someone saves him.
Amber is in L.A. with f(x) because they decided to take a 3 week break. In the first week, other people visit them. They all decide to have a get together party but when Amber is coming back from a store and sees someone walking into the crosswalk without looking, she does something without thinking.
(I'm like telling you the whole story but oh whale. XD)