The baseline mystery of Steven Soderbergh’s masterful Hitchcockian thriller “Side Effects” is “What’s really going on here?” The film keeps viewers emotionally invested yet intellectually off-balance, suffusing even the most ostensibly straightforward scenes with a sense of free-floating anxiety. It pays off with edge-of-the-seat chills, walloping surprises and an uncanny ability to make complex plotting digestible.

Rooney Mara plays depressive Manhattanite Emily Taylor, whose husband, Martin (Channing Tatum), following a stellar Wall Street career, was convicted of insider trading. Now freed, he attempts to rebuild their damaged marriage and restart his career. Hollow-eyed Emily asks her psychiatrist, Dr. Jonathan Banks (Jude Law), to prescribe Ablixa, a promising new antidepressant. After a due-diligence check-in with Emily’s former therapist (Catherine Zeta-Jones), he agrees. Of course, any psychopharmaceutical comes with side effects such as disorientation — and possibly murder.

You might suspect that Soderbergh, who often makes corporate malfeasance a theme of his work, is revving up for an indictment of the drug industry. “Ablixia” kind of sounds like “oblivion,” right? But thanks to a tremendously crafted, diabolically twisty script by Scott Z. Burns (“Contagion”), almost nothing plays according to expectations. The film drops weapons-grade reversals on its characters and the audience, as well. Several times we have to recalibrate, digesting the surprise that the movie we thought we had been watching is not that at all.

What happens when Emily is swept into the legal system, charged with a capital crime, is the framework of the story, but turbulent mysteries swirl beneath. Is there an alternate explanation for Emily’s erratic behavior? Is Martin, a convicted swindler, truly the reformed man he seems? Has success-hungry Jonathan compromised his medical ethics as a highly paid Big Pharma consultant? What is the perfect smile of Emily’s former therapist concealing? It’s hard to choose a dog in this fight.

Even the ominous way Soderbergh sends his camera crawling down corridors hints at hidden motives around every corner. His chilly, ruthless ingenuity is ideal for a story that doesn’t surrender all its secrets in the coming-attractions trailer. It’s no coincidence he opens his film with a slow, insinuating zoom into a distant apartment window, like “Rosemary’s Baby” and “Psycho.” If you can’t make it to the theater before the film starts, do yourself a favor and catch the next complete screening. You’ll never get up to speed otherwise.

The film is terrifically well cast. Mara, in her first role since David Fincher’s “The Girl With the Dragon Tattoo,” has a mysterious, withholding quality that could belong to a wounded emotional zombie or a secretive femme fatale. Hale and hearty Tatum and ice-queen Zeta-Jones play against their defining characteristics in unexpected ways. Law is the best he’s ever been, as a healer with a troubling background and a go-for-the-jugular survival instinct. See it by all means — especially if you love “Body Heat” and “The Usual Suspects” — but be careful who you trust.