"Also, we're constantly jumping around as far as the chronology of the story goes, and that's probably the biggest challenge, just being present and aware of where exactly this moment takes place in the overarching narrative. Things like how does this scene play into how the audience will perceive this little clue; how does Ben view a particular character's actions and how do I play that so the audience can piece things together without giving away too much?"
Henderson says keeping track of all those elements "can be a bit of a Rubik's Cube sometimes", something he and the series' two directors - Kate Dennis and Peter Salmon, a fellow Kiwi - discussed constantly through the whirlwind six-episode shoot.
Because the story is shown through Ben's eyes, Henderson is in every scene, so the production has been gruelling physically as well as mentally for the actor.
At the same time, he says, it has been one of the most rewarding aspects - instead of the usual stop-start, "hurry up and wait" rhythm that screen work normally involves for actors, this one has been all go.
"Working every day, all day is also quite thrilling, because it's quite rare," he says. "Even when you're doing a one-man play, you maybe rehearse for a month and then you're just doing it an hour or two a night. But every day for 10-12 hours? It's quite a treat. It's like an acting workout."
Henderson admits he had to be prodded by his agent to read the script for Secrets & Lies' first episode. "To be honest, I didn't really take it seriously,"he says. "It was from a production company [Hoodlum] I hadn't heard of and it was based in Brisbane, and I couldn't think of a single TV drama that had ever been made there.
"And, you know, sometimes you just dread reading scripts; it's like the chef who doesn't want to cook at home."
Still, when he did finally plonk himself on his couch in Los Angles and crack open the screenplay by Australian Stephen M Irwin, he was "totally hooked by page 10," he recalls.
"I read it cover to cover, put it down, sent an email requesting the scripts of more episodes and they sent me the next two.
"It takes place over Christmas, so there's all the typical seasonal family stuff going on against a backdrop of oppressive humidity and heat, and then there's this heavy, dark, mysterious subject matter.
"It's just a great whodunit with really great relationship dynamics between my character and his kids and wife and the cops, and the way the whole thing unfolds is really delicately done.
"Fingers crossed, if we manage to get what was on the page on to the screen, I think it's gonna be really good."
Henderson has had a varied career, something he puts down to an intrinsic openness. "I think I'm fortunate as an actor in that I do seem to get opportunities to play roles that aren't necessarily typical of what I've done before," he says.
"I think it's part of my personality - I love to travel, I love different cultures and philosophies and perspectives on things."
Now, Henderson is on the look out for a comedy or two, "because the one thing
I haven't really done is lighter stuff. Everything tends to be pretty serious".
He is also keen on the idea of coming home to New Zealand for work - "make sure you write that anyone interested should contact RGM, my Sydney-based agent," he laughs - although not a return to Shortland Street.
"Good memories, though," he says of his stint on the soap's first three years.
"It was such an exciting time to be part of something that allowed us to see ourselves on screen five nights a week for the first time."
