The star of the film is 9-year-old Caine, a precocious little boy who spent his summer vacation at his dad's used auto parts shop in East Los Angeles.
To pass the time, Caine -- who loves everything about arcades -- started building his own arcade entirely out of cardboard boxes, eventually taking over almost the whole store, while his dad sold auto parts on eBay in the back.
The first game was a basketball game with a little plastic hoop that he got at Shakey's and taped to a cardboard box. He also made a soccer game with two little plastic green army figures acting as fixed goalies, and he even created a claw machine with an s-hook and a piece of yarn.
Since school started back up, Caine's Arcade is only open on weekends, when Caine gets out his turquoise Caine's Arcade T-shirt that he designed himself. It says "staff" on the front and "Caine's Arcade" on the back.
Caine charges $1 for four turns at the arcade, but for $2 you can get a handmade fun pass that allows you 500 turns for one month.
When you win a game, Caine will climb inside the box and push tickets out a slot. The prizes include his old matchbox cars, silly sunglasses and bubbles.
He also attached calculators to each box, which he uses to verify the validity of the fun passes he sells.
In other words, it's just like a real arcade, except a million times better.
Mullick discovered the homemade arcade when he fortuitously stopped into Caine's dad's auto parts store to get a handle for his '96 Corolla. Smitten with Caine and the arcade, he asked Caine's father, George, if he could make a film about the arcade and the answer was yes.
But the father warned the filmmaker that Caine doesn't get many customers.
"Well, actually, it's kind of like a joke around here because you are his only customer," he says in the film. Well, Mullick changed all that.
In the film, he explains how he decided to create a flashmob of people who would arrive at Caine's Arcade eager to play some games.
He created a Facebook event for the mob, which got posted on Hidden LA, and then got posted on Reddit, and suddenly people from around the world were lamenting that they weren't able to go to Caine's Arcade.
It's worth watching the video to see Caine's reaction to the crowd of people lined up outside of his cardboard arcade, but we suggest you have a box of tissues nearby.
When it was all over, Caine told his dad that it was the best day of his life.
And if this story isn't sweet enough, Mullick set up a scholarship fund for Caine, which has already raised more than $80,000.