Hasty letter is a cut paper note in the Fallout 4 add-on Nuka-World.
Damn these raiders.
They took Nuka-World and pushed out or enslaved the traders there. It's too dangerous for me to stay here any more, but there's no way I can take the cats with me.
If you are reading this and have somewhere safe, please give Luna and Katana a good home.
The note can still be found in the test cell location TestDrew.