"Marvel's Agents of S.H.I.E.L.D." drew boffo ratings for the series' Sept. 25 debut on ABC. Now it looks like the Strategic Homeland Intervention, Enforcement and Logistics Division is here to stay. That raises questions about the shadowy espionage outfit.

The series stars Clark Gregg as Phil Coulson, the soft-spoken, ultra-competent agent who's been ubiquitous in the Marvel movies. ABC originally ordered 13 episodes, but recently extended the contract to 22 — a full season. The show had a well-attended panel at the New York Comic-Con last weekend, starring writer and executive producer Jeph Loeb and actors Elizabeth Henstridge (agent Jemma Simmons) and Iain de Caestecker (agent Leo Fitz).

At the risk of becoming persons of interest, let's look at some of S.H.I.E.L.D.'s secrets.

Q: Does S.H.I.E.L.D. exist in Marvel Comics?

A: Yes, but it's never been able to hold a title for long. The organization made its debut in a book titled "Strange Tales" in 1965. The first issue introduced the helicarrier seen in "Avengers" and flying cars, like Coulson's beloved Lola. But while S.H.I.E.L.D. never has been a big seller, it's always been a big concept, tightly wound through the fabric of the Marvel Universe. The "Strange Tales" run gave us big bads like Hydra and Advanced Idea Mechanics (A.I.M.), as seen in "Captain America: The First Avenger" and "Iron Man 3," respectively.

Q: Isn't Agent Coulson dead?

A: He was quite thoroughly perforated in "Avengers," wasn't he? His return is one of the series' many mysteries, unmitigated by Coulson's sketchy explanations about being revived by medical personnel and recuperating in Tahiti.

Coulson has mentioned three times that Tahiti is "a magical place." Because the show's creative mastermind Joss Whedon ("Avengers," "Buffy the Vampire Slayer") never puts anything in without a good reason, the repetition means there's something more to the line.

The first episode also has some puzzling dialogue. After Coulson drops one of the Tahiti lines, a medical agent says to agent Maria Hill (Cobie Smulders), "He really doesn't know, does he?" To which Hill responds, "He can never know."

That has given rise to theories that Coulson is an LMD (Life Model Decoy), one of the sophisticated androids introduced in 1965, or even the Vision, an android in the comic-book Avengers.

Q: Are the agents on TV the same as in the comics?

A: No. All of Coulson's agents are original to the show. Which doesn't mean we won't see any comic-book agents eventually, such as Clay Quartermain, Jimmy Woo or even Timothy Aloysius "Dum Dum" Dugan, a World War II vet we've seen as a young man in "Captain America: The First Avenger."

As for the new agents, "there's a reason that these people have been put together," Henstridge told MTV.com. "And we'll find out exactly what that is, even the characters don't know. But they've all had interesting paths to get that point."

Henstridge expounded on that at New York Comic-Con. As reported by insidetv.ew.com: "Well, now we have more episodes to explore the character backgrounds. ... It's going to come organically with the story, but there's lots of secrets and choices of their past that you'll find out."