- Speak to Aventus Aretino inside the Aretino Residence in Windhelm.
- Kill Grelod the Kind in the Honorhall Orphanage in Riften.
- Return to Aventus for your reward.
Questioning innkeepers, asking citizens of Riften, talking to the orphans, mentioning the Dark Brotherhood to certain Thieves Guild members and overhearing talk within Windhelm will clue you into a rumor about a small boy attempting to perform ‘The Black Sacrament’. You will then be granted a miscellaneous quest to go speak to Aventus Aretino at the Aretino family home.
Travel to Windhelm and speak to Aventus Aretino inside the Aretino Residence, which is up the road to the right of the main gate. It’ll be easy to find, as two citizens will be talking out front, a boy and his Dunmer caretaker. Inside, you will discover the Black Sacrament being performed. The Sacrament is designed to gain the attention of the Night Mother and summon the Dark Brotherhood to contract an assassination, and Aventus will mistake you for a Dark Brotherhood assassin. Subsequently, he will request that you assassinate Grelod the Kind in exchange for a “valuable family heirloom.” If you have already killed Grelod, he will be suprised that the Brotherhood is even better then he expected, fullfilling a contract before it is made.
Upon arriving in Riften and visiting the orphanage, you will discover that Grelod’s namesake does not ring true, and that the towns folk call her ‘kind’ as a way of mocking her. Constance Michel does her best to take care of the children, but Grelod ultimately always wins, making the children’s lives as miserable as possible, and not even letting them up for adoption. Because of her universal hatred, killing Grelod does not incur a bounty or any crime, and can thus be murdered in whatever fashion with no chance of a fine or guards attacking you. Note that Constance will always panic once Grelod dies, whereas the children will celebrate her death. With that done, return to Windhelm and speak with Aventus to receive your reward; a family heirloom, which is a dinner plate with a value of 100 gold.