Since they’re still planning on showing Capaldi’s Doctor realize where he’s seen his new face before…I really hope this happens (but I know it won’t).
He needs to return to Pompeii and realize that Karen Gillan was there. He needs to use his old fob watch for some reason or another, but sees the TARDIS and has this overwhelming urge to take it/buy it.
Why’s Amy there? Because, loving The Doctor, she (and possibly Rory) lied to him to spare his feelings. They created a story in which they lived happily ever after, and they made sure he would eventually here of them living happily ever after.
In reality, the Weeping Angels needed to send Amy back in time. The only way to get to her would be relying on her love for Rory. The Weeping Angels sent Amy back to Pompeii, a land where a volcano emitted smoke/ash that allowed people to see into the time (that was the whole point of soothsayers).
Of course, Ten is there and does his thing, but he can’t stop the volcano from killing everyone (save himself/Capaldi). However, it turns out that not everyone “died.” Many people turned to stone from the massive heat caused by the volcano’s eruption, resulting in Amy Pond, the Doctor’s best friend and the person who watched as he figured out how to stop the grand plan occurring in Pompeii, becoming the very first Weeping Angel.