What can I borrow? What's plagiarism?

Among the many swell things about Dashiell Hammett’s writing are the striking, powerful original scenes he brings to life.  One such scene that has long fascinated me is the section in Red Harvest, in which the Continental Op and Dinah Brand get drunk on gin and laudanum.  When the Op wakes up, his hand is on the handle of Dinah’s ice pick.  Dinah’s dead, the needle sharp blade of the ice pick buried in her left breast.  He’s had a blackout and doesn’t remember what happened.  Did he kill her?  If so why?  If he did, does that make the Op just as immoral as the murderers in the town he’s trying to clean up? 

Good questions, and the Op, who narrates in the first person doesn’t know the answers, and doesn’t tell the reader what he thinks happened.  I’m working on a new story that puts P.I. Frank Swiver in a similar situation. 

Then I got to thinking—is that plagiarism?  Can I do that?  What if my readers don’t know that I took the idea from Red Harvest?  What if they do?

Then the other day, I saw a book review in the Washington Post of a new novel, Alena.  Reviewer Carolyn Parkhurst writes, “…Rachel Pastan has taken on a daunting task: borrowing the basic story of Daphne du Maurier’s Rebecca…It’s a tricky business, reimagining a much-loved work of literature.”  Well, good, “re-imagining” is a much kinder word than plagiarizing. 

So I guess authors do that all the time—maybe you can use ideas, plots, characters.  Just don’t steal the language.  (OK, so the opening line of Alena is “Last night I dreamed of Nauquasset again.”)

At any rate, I am going to proceed with my story.  Yes, it’s inspired by my reading of Red Harvest.  But it’s really not the same plot, nor the same characters.  And it won’t be Hammett’s words.