What makes the Showtime spy series as definitive about Here and Now as John le Carre books were about There and Then? Take a look at the second season’s first episodes, and you’ll see it in a nervy concoction of writing and acting.

After a rest, Carrie Mathison (Claire Danes) is back with the CIA. She is summoned to Beirut to reconnect with a source she recruited years before. In the field again, Carrie takes one too many risks, swinging anew on the bipolar pendulum. Weaving through a crowded bazaar, she slyly eludes a pursuer. Just as she turns away, the camera catches her eyes. Framed by a head scarf, they are lit up; Carrie is feeling renewed and redeemed. A less deft director would crowd the actress’s face; a more frenetic writing staff would speed to the next calamity. But the kinetic Danes is allowed a stolen moment of clarity in this era’s blur of secret dangers.

Political shows are often more staffed than inhabited, and “Homeland” is dominated by two of its fraught main characters – Carrie and her person of interest, Nicholas Brody (Damian Lewis). For latecomers, let’s keep last season’s twists under wraps. Suffice it to say: The agent with deep suspicions and the war hero with the al-Qaida contacts are headed for another collision.

Last season, he refused to self-destruct and is now a congressman, while she blew up her career and now grades blue books as an English language instructor. Still, the two are free radicals in search of a tight bond.

The “Homeland” creators have invested in cagey characters but also in the audience’s intelligence. The new season, which begins Sunday night, looks ahead to a gloomy and looming scenario – Israel attacks four of Iran’s nuclear sites, and throughout the Middle East, enemies of the West rise up. That geopolitical tremor is all too plausible. Later, a story line that finds a radical Sunni Muslim terrorist in cahoots with the Shiite Hezbollah movement is less believable.

More than world events, it’s Brody and Carrie who give the series its combustible ingredients. As revealed in season one, Brody embraced Islam while a captive and his traumas convinced him that he had no other solace. Shrewdly, the writers employed a drone strike to radicalize him.

Viewers can better evaluate Brody’s devious behavior because they’ve seen the young corpses he has seen. Similarly, Carrie devolved into an erratic, rule-breaking rogue in last season’s sweat-flecked finale. And viewers stay connected to her throughout; for all her fluttering impulses, she pinned pieces together to make a world-rocking discovery.

The new season adds fire under some simmering story lines, but never to the temperature of potboiler ridiculousness. Is Mandy Patinkin’s Saul all that he seems – a mentor as calming as Robin Williams in “Good Will Hunting”? Will Brody’s fellow Marines accept his reluctance to investigate the death of Tom Walker, the sharpshooter whose aim was off? Will viewers balk at the arrival of a duplicitous journalist with ties to terror leader Abu Nazir and some sway over Brody?

Washington should be more of a character in the drama, and its architectural shadows are so absent they’re glaring. While Israel stands in for Lebanon in some pricey location shots, sleepy Charlotte barely captures the federal city’s grandeur, especially when bullets zipped through what is called Farragut Square. No one needs the skyline cliches of dome and obelisk, but the show lacks some breakneck rush across the Key Bridge.

No one has given such chase since Angelina Jolie in “Salt.” Carrie runs like she’s vulnerable, her blond hair literally grazed by bullets. It is female heroism made more arresting because she is often on the brink of collapse.

This season, lesser characters are gaining strength. Brody’s whiny and intrusive daughter Dana (Morgan Saylor) has something to say about tolerance. She complicates the garden-party ambitions of her mother (Morena Baccarin).

No one can perceive any ideological belief of the vice president (Jamey Sheridan) other than that he believes he deserves to be president. The series exhibits no obvious partisan agenda except to be conservative in its worry about enemies abroad and to be liberal in what the writers have called “spending narrative capital.” Events unfold briskly, even if Brody’s flirtation with higher office happens mere moments after he has achieved lower office.

“Homeland” insists that entertainment can offer escapism not just from ordinary life, but also from ordinary headlines. There’s no hegemony on what’s happening in the world, and there are more official sentries than ever standing in the way of facts. Through the well-traveled characters of Carrie and Brody, the globe seems more curved and spins more quickly.

Above all, “Homeland” depicts something useful and suspenseful about the world that you can’t get anywhere else.