RKO didn’t have the courage of its convictions. Having bought the rights to Francis Iles’ novel, and despite Hitchcock’s insistence on sticking with the original ending, neither preview audiences nor the studio were ready to accept Cary Grant as a murderer. So its present ending was hastily written and shot. It completely subverts all the fine work that’s gone before. Johnny is seen throughout the film as the bounder he is. No one watching him could believe anything else.

Joan Fontaine was a brilliant actress and valiantly, passionately, breathlessly tries to make the shockingly amateurish dialogue in the final scene work — “Oh, Johnny! You were going to kill yourself instead of me, like the audience and I have thought for the last 90 minutes! Oh, Johnny! It’s as much my fault as it is yours! Oh, Johnny! I was only thinking of myself . . . ,” etc.

Cary Grant does his best with this final abomination of a climax. “Lina! Lina! How much can one man bear! When you and the audience thought I was in Paris murdering Beaky I was really in Liverpool!” Etc. Huh!

In other words, this beautifully produced, directed, acted and written psychological suspense thriller turns out to be about a charming lazy n’er-do-well who’s sponged and embezzled his way through life, who marries a beautiful but neurotic aristocrat who, from day one, increasingly assumes the worst about her husband — convincing herself (and us) that he’s killed before and now is about to kill her?

“Just kidding,” the tacked-on final scene says. “It was all innocent. You eating popcorn out there in the dark, and Lina, should be ashamed for even THINKING such things! Go home now.”

It helps, out of self-defense, to watch “Suspicion” with the original ending in mind. Yes, the milk is poisoned. Yes Johnny killed Beaky in Paris. Yes, he’s a psychopath who lies, cheats, steals and kills. Yes, Lina believed him and loved him deeply — the only man she’s ever loved. Yes, her life is no longer worth living, now that she knows the truth about Johnny. Yes, she rightly suspects that milk is poisoned. So she writes a letter to her mother, telling the truth about Johnny’s exploits, and that he is poisoning her as she writes — and that she intends to die. She seals the letter and gives it to Johnny to mail. She drinks the milk. Johnny leaves and unknowingly drops Lina’s letter into a mailbox, thus sealing his fate.

THAT’S a rewarding ending.

It also makes everything that’s gone before (including writing, directing, performances and cinematography) plausible. It gives “Suspicion” a reason to exist.

But that’s the novel’s ending.