Secrets of the Key is a common Instant card from Innistrad: Double Feature (DBL), collector number 73. Current market price: $0.34 (foil $0.12), TCGplayer market prices via Scryfall.
Investigate. If this spell was cast from a graveyard, investigate twice instead. (Create a Clue token. It's an artifact with "{2}, Sacrifice this token: Draw a card.") Flashback {3}{U}