Acting in the Dark

When an actor is not told something that will happen later to avoid having it possibly affect the way they play the character currently.

For example, an actor in a Spy Drama receives scripts only an episode ahead as shooting proceeds. They are playing as a goodie and do not know why other characters are dying. Then another script comes along—and they discover that they were evil all along.

In most shows the writers have at least an outline of what's going to happen, if not a complete set of scripts. This trope is for when even that outline is not communicated to actors. It covers cases of things their character would know (see above) and cases where their character wouldn't know the later developments (such as their character getting hit by a bus.)

Another reason to do this would be to prevent a disgruntled or loose-lipped actor or crew member from letting slip major spoilers.

Compare Enforced Method Acting.

Examples of Acting in the Dark include:

Anime and Manga

Fullmetal Alchemist: Vic Mignogna has told fans that he did this on purpose while filming so his reactions as Edward are genuine; for example, his shock at arriving in our world in the 2003 anime version's penultimate episode. He did it again in Code Geass.
An in-universe example: It's what the director in the movie Perfect Blue does to his actors, making the parallels between the main character and the character she plays in the movie even creepier as both start to suspect they are the killer.
Gen Urobuchi, writer of Madoka Magica, did not informed Emiri Katou, voice actress of Kyubey, show's mascot, of her character's true nature and kept character designer Ume Aoki in the dark about show's dark storyline. He either wanted to make sure the viewer will get fooled, in which case it was this trope, or he really wanted to see their faces once they'll find out, in which case he was just trolling.

Film

Slim Pickens, who famously played the B-52 bomber commander and pilot in Dr. Strangelove, was not told that the movie was a comedy during filming, and played his part straight.
Ben-Hur: A hilarious and confusing example occurred in the epic. The film features a very deliberate subtext suggesting that the two main characters, Judah and Messala, were lovers in their youth. Stephen Boyd, who played Messala, was told about this dynamic between the two characters. Charlton Heston, who played Judah, was not told about the relationship for fear that he would freak out.
- Which is a brilliant example (and mentioned in) Enforced Method Acting: Messala comes across as someone trying to rekindle the relationship while Judah is uncomfortable because he'd prefer to forget it happened and doesn't want to be reminded of it.
Inverted for the Harry Potter movies. Alan Rickman (Snape) was one of the few people in the world who Rowling told about the ending ahead of time so that he would know the true motivations behind his character.
In The Blair Witch Project, actors weren't given instructions until the beginning of each day of filming (most dialogue was improvised). They also weren't told when they would be "attacked" at night, so those moments were genuine surprises.
Blazing Saddles: Mel Brooks used a musical version of sorts when he got Frankie Laine, who originally sang the Rawhide theme, to sing the theme. Brooks wanted Laine to sound like this was a genuine, dramatic cowboy movie, and so completely "forgot" to tell him about the comedic nature of the film, to the point that Laine didn't realize the truth until he actually saw the film at his local cinema. He consequently produced such an epic cowboy movie song that it's sometimes played alongside other classic cowboy movie themes non-ironically.
Scream 4: During initial filming, the actors only read the first 75 pages of the script so that not even they would know the identity of the killer until the time came to shoot The Reveal.
- Craven also hid the final pages of the second movie's script.
In The Empire Strikes Back, no one was told about Darth Vader's revelation until just before shooting the scene. And by "no one", we mean James Earl Jones (who initially thought it was a lie) and Mark Hamill (who was pulled aside and told the truth, and also didn't believe it): George Lucas wanted so badly for this to be a secret that the scene was filmed with David Prowse saying, "No, Obi-Wan killed your father!"
- Prowse was very upset after the premiere, and told Lucas his body language would have been completely different if he'd known the truth.
In the film Smile, none of the actresses playing the pageant contestants were told who the winner was until the scene was being shot.
In The Shining, Kubrick was able to film the whole movie without the young actor playing Danny Torrence being aware that he was in a horror film. Pretty amazing, considering ever-darkening tone of the film and some of the horror scenes he is in.
The actresses for the main cast of The Descent were not told about the crawlers. When they finally met one in the movie the first take was of them all running off the set screaming.
Legend has it that during the filming of Casablanca, after each scene was filmed, Humphrey Bogart and the writers would sit down together and decide what should happen next. Ingrid Bergman had no idea until the very last scene was filmed whether her character would leave with Victor or stay with Rick.
According to Kevin Spacey, none of the actors were told of the ending of The Usual Suspects while filming.
- Gabriel Byrne was led to believe that his character was Keyser Soze. After he saw the finished product, a reporter asked him who Keyser Soze was. He replied "All throughout filming and up until tonight, I thought I was."

Live Action TV

Harper's Island: The actors were not told who the murderer was, with the murderer's portrayer himself being kept in the dark until about half-way through. Co-executive producer Karim Zreik, had the job of informing the actors in this death-laden 2009 Miniseries just when their time was up. The actors gave him the nickname Karim the Assassin.
- Specifically, the character who turned out to be the murderer (Henry, the character played by star Christopher Gorham) wasn't told he was the bad guy until eight episodes into a 13-episode season.
24 thrives on this one. Notably, Sarah Clarke was not told that Nina would be the Season One mole until about episode 12.
Lost.
- Matthew Fox (who plays Jack Shepherd) has stated that he was the only actor on the show who knew how the series would end before the production of the final season.
- In an interview with Michael Emerson, Emerson confirms that the cast was Acting in the Dark. One assumes that getting answers like "I can't discuss that" happened early and often on the Lost set..
- Terry O'Quinn was not informed that he was no longer playing Locke in season 5 because he was meant to act consistently with what was known until the reveal.
Parodied in the Hancock's Half Hour TV episode "The Bowmans", where Hancock is a radio actor and is shocked when he gets a script that kills off his character. (He gets his own back in the end.)
House: During the season 4 "reality show" where House was whittling down the candidates as the episodes went on, those who would not make the final cut were not told until the week of filming for that episode began.
Babylon 5 did this with, well, everybody. Specifically to avoid the actor getting influenced by Character Development, since these changes were caused by organic growth. It was supposed to be a gradual change, and it worked. Characters weren't "revealed as suddenly evil" so much as gradually became as such.
In Season 5 of Buffy the Vampire Slayer, the actor playing Ben wasn't told the exact nature of Ben's relationship to Glory until very late in the game.
Similarly, on Dollhouse, Harry Lennix wasn't told that he was the Big Bad until the middle of the second season.
M*A*S*H (television) did this with the departure of Henry Blake. The whole episode was filmed with the entire cast being under the impression that Blake was going home to America. After they filmed Blake's departure, the cast was given a changed script for the last scene: Radar delivers the news that Blake's plane was shot down with no survivors.
Justified: During most of Season 1, the audience was wondering if redneck racist Boyd Crowther had really Found the Lord and become a (fairly nutty) backwoods preacher, or was just scamming everyone. It turns out Walton Goggins, who played Boyd, didn't know either. In this case the writers/producers did this to force him to play it ambigiously.
Star Trek: Deep Space Nine: Alexander Siddig only found out that his character was actually a Changeling impersonator for several episodes until the episode where it was revealed.
Another Inversion- On Doctor Who, Alex Kingston was the only person aside from Steven Moffat that knew the extent of River Song's arc and the events which occurred in it before the readthroughs.
On Curb Your Enthusiasm, the actress Cheryl Hines is usually unaware of what the character Larry David has gotten himself into during an episode.
Twin Peaks. David Lynch had planned out the identity of the killer of Laura Palmer long before the big reveal, but he didn't tell the actor until the time came to actually shoot said reveal.
The writer of Forbrydelsen writes as he goes, so that neither he nor the actors know who the killer is going to be until the final episodes.
In season six of Dexter, only Edward James Olmos knew that his character Professor Gellar was Dead All Along and a delusion of his "student" Travis. Even the directors were kept in the dark, leading to a few instances where Olmos had to gently nudge them away from filming a scene in a way that the reveal wouldn't make sense.