A masked gunman roams the hallways of Dartmouth Middle School.
But it's only a drill.
He's eventually caught by a SWAT team and taken into custody.
The tense minutes of the hunt were played out over computer monitors at the school and at the Dartmouth Police Department through a system called Mutualink.
"It's the gel that brings disparate communications systems - radio, video, public address, it brings them all together on a common operating platform," said Jeff Kelly of Mutualink.
When school administrators realize there's an emergency, someone hits a designated panic button. Instantly, the school cameras and public address system can be seen at a police dispatcher's desk, putting someone who would otherwise be on a radio, in the school's halls, and in the case of Thursday's drill, following the gunman's every move.
"It cuts our response time in half. It gives the officers who are responding as much information as they can possibly obtain," said Dartmouth Police Chief Timothy Lee.
The Mutualink system is being used in stadiums, shopping malls, and even helped in the aftermath of the Boston Marathon bombings.
In Dartmouth, every school is wired making it the first kindergarten through 12th grade system in the country to adopt the communication network.
"Any system that we have in place to prevent something from tragically happening is a huge plus," said Dartmouth Middle School Principal Darren Doane.
The system cost the town a little more than $100,000.