The title says mostly everything, you're the first girl to show up in the maze, what happens when you meet a certain someone? ( This takes place before Thomas arrives, so yea.)
Marcie was the first girl to arrive in the maze full of boys, a glitch in the system was what was assumed until another girl came up, however that was also when the end was declared and the entire life that she remembered was turned upside down. She travels from the Glade through to the last city dealing with death, a deadly virus, a possible cure and love.