Marvel Studios chief Kevin Feige says the red in the ledger of super-spy Natasha Romanoff (Scarlett Johansson) will be declassified in Black Widow, where audiences will learn the meaning behind Loki’s (Tom Hiddleston) taunts in The Avengers. In the 2012 blockbuster, the agent of S.H.I.E.L.D. tells a jailed Loki, “I got red in my ledger. I’d like to wipe it out.” The taunting trickster questions if she can “wipe out that much red,” referring to secrets pried from a brainwashed Hawkeye (Jeremy Renner) when he presses Romanoff about “Dreykov’s daughter, São Paulo, the hospital fire … Your ledger is dripping. It’s gushing red.”

We all agreed that we had to find out what happened in Budapest. That started out as this throwaway line which Joss Whedon threw into Marvel’s The Avengers as a funny moment between Hawkeye and Black Widow. That’s Clint and Natasha talking about their history, and you get a fun little Easter egg for fans to theorize about. We thought that if we don’t go back to Budapest and find out what really happened there, people will feel unsatisfied. I wondered what did happen there?

We often talked about what is going on in Natasha’s head. I really think that Natasha is haunted by the fact that she has this past that she feels so guilty about. Unfinished business is that sense of guilt that follows her around, which all stems from what happened in Budapest. Black Widow is not about what happened in Budapest, but it’s a huge jumping-off point for us to understand the heaviness of Natasha’s burden.