A woman and three children play hide-and-seek in the snow outside a patrician brick mansion. Inside, her husband opens the morning paper and discovers a fresh four-leaf clover, which according to - means - . Moments later, he points a gun at his head. Outside, his wife hears a single gunshot.
The same day in Lower Manhattan, Will Travers arrives at the American Policy Institute, a federal intelligence agency. Tanya MacGaffin, a fellow API analyst, asks for help solving a crossword entry. Will supplies the answer: Marsilea quadrifolia, the Latin word for four-leaf clover.
From his office window, Will observes a man (David Hadas) exit a car and sidestep the "13" painted on the adjoining parking space. Will's coworker Maggie Young enters his office and quizzes him about the date. It's his birthday, Will realizes. Maggie invites him to lunch.
Will and three other analysts -- Tanya, Miles Fiedler, and Grant Test -- enter a conference room. Grant chides Tanya for failing at what he considers her "most important job," remembering the doughnuts. David Hadas, the team’s boss, and the superstitious man Will observed, bustles in bearing the team’s assignments. Will's involves a Russian missile broker named Yuri, - and -.
At lunchtime, Will declares himself too busy to join Maggie, then sets his work aside to peruse several daily papers' crossword puzzles. Later, he informs David he has found identical references to the three branches of government across several papers. The clover entry, Will theorizes, is related. "What or who does that fourth leaf represent?" he asks.
David dismisses the references as a joke among crossword editors, but notifies his boss, Kale Ingram. "Anybody else see this?" Kale asks. "No," replies David.
In the cafeteria, Miles and Grant give Tanya, a recent hire, the lowdown on her colleagues. Truxton Spangler, the agency's unapproachable director, for instance, eats cornflakes for lunch every day. "Why is Will Travers so mopey?" Tanya asks. Miles replies that his wife and child died on 9/11 and Will had been scheduled at the World Trade Center that morning, but arrived late. "He's never been late for anything since," Grant says.
Will grabs lunch at a street cart where David joins him. Will expresses doubts about his job and hints at resigning. David gives him a birthday present, a guide to road food. "I don't blame you for taking stock," says David.
The problem isn't his work, Will says, but rather being unable to discuss it. "That's the hardest thing in this job," David replies. David invites Will to dinner. Will declines. "Days like these," he says, remind him of his family. "I miss them too much."
As he departs, David hands Will an envelope and says, "Don't open it until you get home." Outside his apartment, Will opens the envelope to find a key attached to this note: "Drive away. Don't look back. It's time."
Will notices a Norton motorcycle parked curbside and calls David. "I can't keep this," he says. "I can hear you smiling," David replies. "Why now?" asks Will. David says that he'll explain everything in the morning. He's taking an early train out of Putnam station; Will is to meet him at a bar.
The next morning, a man dressed similar to David (but whose face is never seen) walks down a train's aisle. Seconds later, a train speeding in the opposite direction switches onto the first train's track.
Will drinks coffee at a bar. On the TV news, coverage of the death of the mansion owner, revealed to be Thomas K. Rhumor, is followed by word of a train collision near Putnam station.
Kale delivers the eulogy at David's funeral. David, it turns out, is Will's father-in-law. After the funeral, Kale offers David's position to Will, who expresses hesitation. "Think it over," Kale replies. “If your mind doesn't change, I'll accept your answer -- and your resignation."
That evening, Will sits in David's office. The phone rings. "Knight to king's bishop three," says the caller, who hangs up after realizing that David hasn't answered. Will locates a chessboard (inside a globe) with a game in progress. An inscription on the board reads, "From one pawn to another -- E.B."
Still that night, Will rings a doorbell. "Are you Ed Bancroft?" he asks the weary man who appears. "David's been killed," Will informs him.
Will tells him around the office that people say, "You were a genius at cracking codes, until the codes cracked you." Will presents the crosswords but Ed claims not to recognize them. "They showed up the day before David died," Will replies. "Coincidence?" Ed abruptly asks Will to leave.
As Will heads home, a man named - shadows him on the Putnam station platform. Will notices David's car in the lot. The man shadowing Will drives away. David's car is parked in space 13.
Will visits Maggie in her home, apologizing for the hour. The superstitious David would never have parked in space 13, Will maintains. "His remains were identified," counters Maggie. Will needs to accept David's death and move on.
At work the next day, Will informs Maggie that he's resigning. This ensures Grant's promotion, she replies. Miles corners Will later and insists that David would want him to "pick up the torch."
When Will unexpectedly accepts the position because - , Kale reacts curiously and asks "What changed your mind?” "You know what? I don't care," he continues. "Let's introduce you upstairs." Upstairs, an aide tells Will that he’ll meet Spangler tomorrow.
Spangler disembarks a ferry and is driven to a country home in [redaction] . He enters a meeting in progress. "Anybody double check that Tom is actually dead?" he asks. "He blew his brains out," replies [redaction] . "I saw his body."
"Good," says Spangler. "We're back on track."