M. Night Shyamalan has proven himself a master of misdirection.

His previous mainstream films, “The Sixth Sense” and “Unbreakable,” provided effective shock endings by expertly diverting the audience’s attention. The creepy “Sense” convinced viewers that the solution to its central mystery resided within a troubled boy, when the real answer lay in the psychologist who treated him. Similarly, “Unbreakable” seemed to be about unlocking the origin of a physically invulnerable man, when the key to his abilities involved the comic store owner who discovered him.

Mel Gibson, left, and Rory Culkin explore unexplained crop circles in the thriller Signs.

Now comes “Signs,” another taut piece of work from the 31-year-old writer/director. Again, Shyamalan fiddles with viewer expectations by ostensibly crafting a global alien invasion tale that ends up being more about one man’s internal spiritual journey.

That man is Graham Hess (Mel Gibson), a grieving Episcopal priest who decided to leave the church after witnessing his wife’s accidental death. No longer interested in giving comfort to his former parishioners, Graham is busy raising his son (Rory Culkin) and daughter (Abigail Breslin) on a farm in rural Bucks County, Pa. Joined by his younger brother Merrill (Joaquin Phoenix), a washed-up minor league baseball star, the family seeks to put their lives together after the tragedy.

Upon finding a crop circle in the huge cornfield behind his house, Graham comes face to face with a host of unexplained incidents, from his pet German Shepherd turning violent to brief glimpses of strange beings. Before long, this phenomena starts spreading to other isolated areas of the world, and the Hess family begins to prepare for what appears to be an other-worldly encounter.

“Signs” exploits fear of the unknown better than any movie since “The Blair Witch Project.” A palpable sense of foreboding lingers throughout this Pennsylvania locale; there’s something about an isolated farmhouse surrounded by 8-foot high rows of swaying corn that is creepy in the first place, let alone when unnatural things are scurrying around in its shadows.

Yet, “Signs” also is the most comical of Shyamalan’s efforts. Whereas his previous thrillers were somber affairs, humor is often used here to alleviate tension, thus allowing it to build back up stronger than before. Phoenix delivers a priceless speech about the evils of nerds. And the two children one of whom hails from the apparently inexhaustible supply of Culkins display eccentric personality traits that the film capitalizes on. (Breslin has a drinking water phobia that would fit right at home in Gibson’s erstwhile flick “Conspiracy Theory.”)

Shyamalan, who is no stranger to working with child actors, also makes allusions to a pair of his favorite boyhood films. He establishes a mounting level of paranoia comparable to “Invasion of the Body Snatchers” and sets up an extended sequence of board-nailing and cellar-harboring right out of “Night of the Living Dead.”

Only during this latter section does the picture start to show signs of uncertainty. Just as Shyamalan’s characters keep retreating until they have no place to go, so does his screenplay. He literally writes himself into a narrative corner from which there is little chance of escape.

The final third of Shyamalan’s script leaves the viewer with far too many questions about the behavior of the Hess clan and their extraterrestrial opponents. Why do Graham and Merrill not arm themselves if they fear an attack is coming? Why would Graham ignore living proof of a creature? Shouldn’t he at least alert authorities to its existence? (His best friend is a cop, after all.) Do the aliens not have weapons that can break down a wooden door?

Also, the way the film comes together the “signs” pertaining to the movie’s title is kind of … silly. It’s a very provincial conclusion for a threat with such planetary repercussions.

“Signs” never quite goes where one thinks it will, which deftly works to keep the audience off-balance. But Shyamalan’s inability to deliver his trademark “startling resolution” ultimately leaves viewers adrift in the wind like so many stalks of corn.