Opening arguments began on Monday in a civil trial about a Broadway musical that never came to be, a real-life drama that, even by showbiz standards, stretched the suspension of disbelief.

The producers of “Rebecca,” a show based on the 1938 novel by Daphne du Maurier, are suing the musical’s former publicist, Marc Thibodeau, in New York State Supreme Court. They say that, without their knowledge, he sent anonymous emails to a last-minute investor in 2012, urging him not to put money into the show. Mr. Thibodeau, a longtime Broadway press agent, has said he was only trying to protect the investor from losing millions in an already troubled production, which ultimately never opened because of a lack of funds.

Mr. Thibodeau has previously been found in breach of contract in a related case; the jury will assess damages for that finding and decide two other claims by the producers, defamation and tortious interference.

Lawyers for the producers said on Monday that Mr. Thibodeau’s actions were a brazen attempt to undermine the very production — a story immortalized in a film by Alfred Hitchcock in 1940 — that he had been hired and paid to promote.