Shadows Behind the Scenes is Chapter 3x of Fire Emblem: New Mystery of the Emblem. This chapter is reached if the player beats Chapter 3 in 24 turns or less on Normal Mode (28 on Hard, 35 on Maniac, 38 on Lunatic). Alternatively, the player can have no more than one ally retreat occur in the Prologue.
Kris, Marth and their other cohorts will start out west, with Clarisse guarding the fortress on the other side of a path weaving through mountains. Wrys will start in the middle of that path. With Knights all over the path, it is unlikely that Wrys can unite with the group before he takes damage. Perhaps the best way to tackle this chapter is to quickly move and overwhelm each individual Knight, having Wrys head west to meet with them as soon as possible. Seizing the fortress to the east will be relatively easy, as Clarisse will flee when approached.
Knights appear from the middle and right forts at the end of turn 4.