Go to Darkdale and speak to Sandy and Sanders at X:327 Y:309. Receive Children's Graffiti.
With the Graffiti in your inventory, get 3 Sugar and speak to Webb near the Drugstore, at X:358 Y:281 in Darkdale. He'll give you a Half-Serving of Roasted Chestnuts.
Note: you need 2 Chestnuts, 6 Sugar for a full serving in TW domo, since the half serving does not work there.
Take the chestnuts to the brothers. They'll tell you Shirley Bree is in Copperhorn.
FIGHT: Go to X:377 Y:347 in Copperhorn Mountain. You have 30 minutes to defeat Shadow (level 30 non-elemental glove Martial Artist, 15778 HP) and 3 Shadow Assassins (level 25 non-elemental staff Martial Artist, 5259 HP).
When they have been defeated, Shirley will reward you.