Story!
Go to the comic shop, look at the robe in the display case and ask the staff lady about it. She'll give it to Agatha if we can get the Enigmarillion, a legendary book.
Go to the library and search the book in the computer upstairs. The book is on 2C in the Art Aisle, so go get it.
If you try to leave the library with the book, the librarian will stop you and tell you that you need a library card, so follow the steps for either "New Look" (if you don't want to spend money) or "Licence to Read" (if you want to spend money).
Anyway, when you get the book, go give it to the comic store lady.
Now we got the robe, but i doesn't fit Agatha, so go to the dress shop and give it to the woman inside. Either give her money or get a burger from the Diner to pay her.
When finished, go talk to Sandro and show him the tunic.