5-year-old's 'Ghostbusters' wish comes true when entire city is transformed

London, 5, has survived three open heart surgeries.

Something strange in the neighborhood happened in Sacramento, California, Monday as a 5-year-old boy with a congenital heart defect lived out his "Ghostbusters" fantasy.

The boy, London, has already survived multiple open heart surgeries due to his heart defect, which was diagnosed 15 hours after he was born, according to the Make-A-Wish Foundation.

"He’ll come out of [what]ever room he’s in, ‘Oh it’s time to hunt ghosts,’ and put on his pack and get hunting ghosts at the house or at the park," London's dad, Stuart Greet, told ABC News' Kanya Whitworth. "I don’t know why he likes it so much, but something about it has really grabbed him."

It was Hudson, the "Ghostbusters" actor, who told London, via video, that he would be joining the "Ghostbusters" crew with a big assignment: Saving the city of Sacramento from ghosts.

Sony, the production company behind "Ghostbusters," outfitted London with official equipment, including a proton pack, PKE meter, Ecto goggles and a uniform with his name on it.

The entire city of Sacramento -- from the mayor to the police and fire departments -- came together to help London fight ghosts.

"It’s great seeing people come together and take care of a kid that they don’t even know," said Green. "It’s making his day so exciting and we’re thrilled about it."

Just like the original Ghostbusters rode the Ecto-1 through New York City, London traveled throughout Sacramento busting ghosts and marshmallow man.

"Best day ever," London told Whitworth.

At the end of his ghost-busting travels, London followed a trail of marshmallows to a stage setup at Sacramento's Waterfront Park.

There, in front of the city's mayor, police chief and fire chief, London was credited for saving the day. His wish was made official when the entire crowd together yelled "make a wish."