Spending three days on set with LL and co-star Chris O'Donnell, the episode centres around a group of hackers being investigated for hijacking a missile test.
Filming took place at LA's Bob Baker Marionette Theatre - the oldest puppet theatre in the US and one which Ang had always wanted to visit.
Having spent time with an LAPD officer in preparation to play a detective alongside Woody Harrelson in Triple 9 last year, Ang already had a strong handle on guns but wasn't prepared for squibbing (being rigged with "explosives filled with debris and blood-like substances") and admits the show's speedy turnaround was challenging. "It definitely felt like I was stepping into a well-oiled machine. People knew what they needed to do, how to make it happen and wanted to make the day then get out - which was really challenging as an actor because as a guest star you're the lowest of priority to be shot.
"So you only get one or two takes, which is terrifying if you're a perfectionist like me. I was like, 'Gosh that felt like a warm-up and I stumbled my line', while they're like, 'Okay, great, moving on'.
"It's super fast-paced."
Though the first day was intense, Ang enjoyed chilling with LL, who plays Sam Hanna, and chatting to O'Donnell about his time in New Zealand in-between takes. "I was probably fan-girling a little too hard. LL is totally chill. He was exactly how you'd expect him to be - talks like a rapper, with that melodic, poetic way of chatting.
"And Chris O'Donnell was super-nice - he's a little older than I expected but I guess it's been a couple of years since he was Robin! His daughter was born in Christchurch and he has spent lots of time in Queenstown, so talked about how much he loved it.
"What was interesting for me was how as a hungry actor in LA, just being able to be on set my energy was really high and palpable, but for these guys this is their nine-to-five. It's not like they're not excited about their jobs, but it was very run-of-the-mill for them."
One of the top five most watched shows in America's 2013-2014 television season, NCIS: LA is one of a string of television roles Ang has enjoyed since relocating from New York to LA, including her lead gig on MTV's Underemployed, a guest role as a Chinese beauty queen on Drop Dead Diva, a stint on Grey's Anatomy and starring alongside Scott Wolf in Perception. "Coincidentally that was the same day I noticed my first grey hair. I was like, 'Oh my God, time flies - Party of Five was so long ago that I now have grey hair!'"
A thriller she starred in, The Taking of Deborah Logan, is still taking the horror world by storm, while an indie film Fallen Stars is also coming up, along with Triple 9 - which remains a highlight. "Woody [Harrelson] is crazy, but in a really awesome way," says Ang, who recently posed for Kiwi label Lonely Lingerie's "Lonely Girls Project" campaign.
"He's a hippie and he lives and breathes it. His trailer is a bus he's converted to run off biodiesel and inside is a yoga floor and vaporiser - you go in and get hit by a plume of smoke. But he's a lovely guy and super-generous.
"He had just come off True Detective and I thought he may be way too elite for me to hang out with, but he was like, 'Come and hang out! Do you want to run lines?'
"I had to keep pinching myself because he's someone I definitely look up to."
NCIS: LA screens Tuesdays on TV3 at 9.30pm.
