SPOILER ALERT: Do not read unless you have seen the Feb. 12 episode of “Homeland,” “A Flash of Light.”

“The truth does matter. I will make it matter.”

With ominous words and a painful image at the very end, season six of “Homeland” kicks into high gear in episode four, “A Flash of Light.”

Suspicions mount all over the place before the stunner of a climax in this disconcerting episode, written by Patrick Harbinson and directed by Lesli Linka Glatter. The delivery van explosion at the end that kills Sekou is a big surprise, and so is the re-appearance of Iranian operative Majid Javadi (played by Shaun Toub), who was last seen in season three being turned into a CIA asset by Saul and Carrie. Javadi was involved in Nicholas Brody’s final mission in Iran, and we all remember how that ended.

The camera never stopped moving in this episode, setting a frenetic tone. And the script was packed with cutting lines. Dar Adal comments on the “striking hair” of Carrie’s daughter, Franny, (who has her father’s ginger coloring) when he confronts her outside of Franny’s school. (Mama Bear Carrie is not amused.)

Carrie tries to give her earnest lawyer partner Reda Kazem a crash-course in realpolitik when he fusses over not knowing the real story of how she secured Sekou’s release from police custody.

“A win is a win. Can’t we just leave it at that?” Carrie advises. Kazem’s moral authority has some sway over her, however, as she sheepishly assures him, “It won’t happen again.”

But the weighty exchange of the episode belongs once again to Saul Berenson, after he’s face-to-face with Javadi after his middle-of-the-night walk from his sister’s home into Palestinian-occupied territory in the West Bank.

Saul is in search of the truth about whether Iran is violating the terms of the nuclear deal, which continues to be bashed in the real world by the Trump administration. The pact ended decades of Western sanctions against Iran in exchange for the country giving up its nuclear weapons development program.

Javadi is cagy, which bugs Saul to no end. Javadi is a prime example of the despicable characters that CIA operatives have to work with in the messy pursuit of the greater good.

Javadi, “Homeland” fans will recall, made a point in season three of executing the brutal revenge slaying of his wife and daughter-in-law, 20-plus years after his wife fled Iran for the U.S. But his visit to D.C. wasn’t a total loss for humanity. Carrie and Saul forced Javadi to cooperate with the CIA after confronting him with evidence that he embezzled millions from the Iranian government. Job One for Javadi was to be an advocate for moderate positions within the government and find a way to dispense with the extremists. In “Homeland’s” world, Javadi’s covert maneuvers helped pave the way for the real-life nuclear deal that has been politically polarizing in the U.S. 

Only Mandy Patinkin could pull off Saul’s breathless entreaty to a man he knows is capable of murdering the mother of his child.

“We started something together three years ago, something that succeeded beyond our wildest dreams,” Saul said.

“We didn’t start anything together, you put a gun to my head to expose me,” Javadi replied.

Javadi wonders why Saul, a seasoned hand at geopolitical chess, is so obsessed with getting confirmation that Iran is running a “parallel program” of nuclear development in North Korea.

“What does it matter? Half your country will wake up tomorrow convinced that we’re cheating. Half of mine will wake up chanting ‘death to America,’” Javadi said.

“I still need the truth,” Saul replied.

“That is the truth. Only you would call it succeeding,” retorted Javadi.

Saul delivered the Berenson Doctrine: “The truth does matter. I will make it matter.”

“Flash of Light” sets up the whodunit that seems will drive the rest of the season: unwinding the truth of the explosion that kills Sekou, a day after Carrie’s leverage play with over-zealous FBI agent Ray Conlin forces the feds to drop their trumped-up terrorism charges.

But no good deed goes unpunished. After his welcome-home party, Sekou goes right back to the webcam on his laptop to post more incendiary statements online. He also finds that his release raises suspicions among his friends that he has become an FBI informant — not a cool thing in Sekou’s social circle.

By the time Sekou gets in his van for his ill-fated early morning delivery run for Medina Medley Mediterranean foods, there are three constituencies who might have had a motive to plant the bomb that explodes as he is driving through Midtown: the CIA, the FBI and Sekou’s unforgiving pals. The latter seems the least likely scenario. His friends might have wanted to beat him up for being a snitch, but a bomb seems extreme.

The FBI and CIA both have ample opportunities to have tracked Sekou and Carrie. FBI agent Conlin, of course, might be mad enough over Carrie’s blackmail to take it out on her client. But the CIA seems the most likely. Dar Adal and Co. have the twin motives of wanting to rattle Carrie and amp up the public’s fear of terror attacks in order to counteract the plans by President-elect Keane to dial back intelligence operations and the war on terror.

“I don’t think you understand how vulnerable you are,” Adal tells Carrie. That would seem to be a little on-the-nose for “Homeland” in terms of foreshadowing Adal’s direct involvement in Sekou’s killing. But the guy who is watching Carrie’s house from across the street — the watcher Quinn has been watching — took a middle of the night trip to the Medina Medley warehouse hours before Sekou’s van blew up. Also, we know that the CIA has planted a listening device allowing Adal to snoop on Carrie’s conversations with Keane. Meanwhile, Quinn is tracking the pattern of lights flickering in Carrie’s home — something that for once probably can’t be blamed on Con Edison.

Regardless of who is responsible for Sekou’s murder, the closing aerial shot of black smoke from the explosion billowing over Manhattan was chilling.

Other observations:

** Quinn and Franny appear to be bonding. “Well, it’s snack time!” she says to him cheerily after she gets home from school.

** Like her mom, Franny is a keen-eyed observer of what goes on around her. “He had painted hair and he scared mommy,” she tells Quinn of Adal’s confrontation with Carrie outside her school.

** Blood is thicker than ideological differences. Saul’s sister comes through in providing a cover story for him when Mossad agent Etai comes to the door of her West Bank home to offer Saul a ride to the airport that he can’t refuse. 

** Mossad plays rough, but they’re not inhumane to an ally. After word of the van blast in New York reaches the Mossad, Etai reverses his plan to “f— with” Saul and detain him in Israel over his clandestine meeting with Javadi. “You’re needed back home,” a grim-faced Etai tells Saul as he delivers the news of the explosion.