Chalk Outline is a uncommon Enchantment card from Murders at Karlov Manor (MKM), collector number 157. Current market price: $0.26 (foil $0.36), TCGplayer market prices via Scryfall.
Whenever one or more creature cards leave your graveyard, create a 2/2 white and blue Detective creature token, then investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.")