A letter shows up in Evelynn's mailbox with the Du Couteau seal upon it's back. Inside in a folded white peice of paper.
You are cordially invited to the birthday gathering for Riven... of Noxus tomorrow, on the date of Sept 13th at the Du Couteau Summer Home on the outskirts of Noxus. No need to bring anything, just send a reply to Katarina Du Couteau as soon as you can.
P.S. you best be on your best behavior... or else.