I'm going to assume they thought Walt was the author who came out of the book?

First of, Walt Disney isn't the guy who came out of the book, he's an author but he's called Issac. When he gets out of the book, Gold gets to him before Emma and co. and bribes him with the special pen he needs to write in the book. Gold needs the author to change his fate because his dark deeds are catching up to him and his heart is turning black, with a tiny flicker of light remaining (his ability to love) which when gone means that Rumplestiltskin the man is gone but the Dark One remains. Now that the author has his pen he needs ink, which he needs dark saviour blood for, which is why Rumple has been trying to corrupt Emma. In order to do this Rumple sets it up so that when Cruella kidnaps Henry Emma is the one to find them and is then put in a position where she kills Cruella to save Henry, looking like she's on her way to turning dark, which comes to a head when Emma and Lily, Maleficients daughter and Emmas childhood friend (if you remember from one of the 4A episode flashbacks, think it was Breaking Glass), are reunited. It turns out that Lily knew all about Storybrooke, who her mother is and what Snow and Charming did and wants revenge which results in Emma and Lily getting into a fight which climaxes with Emma pointing a gun at Lily and Regina talking her down. Emma then tells Lily that she's going to reunite her with Maleficient. After this Emma, Regina and Lily head to New York to save Robin and Roland from Marion who, plot twist, has been Zelena the entire time! She went back in time with Emma and Hook in the 3B finale, killed the real Marion when Emma and Hook left her unguarded and glamoured herself as Marion, basically to destroy Reginas happiness. w