A boy sits in a high school library scratching a phrase in blue ink into a desk. “I am bored,” he writes.

Later, when he returns to the desk, he finds an unexpected response: “Hi bored, nice to meet you.”

For what seems like days, the boy and his mysterious respondent scribble messages back and forth.

“What are you up to this summer?” he writes.

“Nothing cool,” a girl replies.

“Maybe we should do nothing cool together,” he writes, as he goes on a quest to find out who she is.

In the end, he runs into her while signing yearbooks in the gym.

But while you’re watching the adolescent love story unfold, you’re missing a dark and deadly drama unravel: Another classmate is plotting to shoot and kill. The student, who is nearly invisible in the background of the shocking video, is being bullied by other teens and showing signs of social isolation.

He’s reading a magazine about firearms and watching a YouTube video about how to shoot them.

He’s posting a disturbing selfie on social media — one showing himself pointing a handgun with a grim message: “See you at school.”

While you’re watching one boy get the girl, another one emerges from the background, storms into the gym and cocks a rifle.

Petrified students unleash chilling screams as they scatter.

Then, the screen turns black.

“While you were watching Evan,” a message reads, “another student was showing signs of planning a shooting.”

A nonprofit group created following the massacre at Sandy Hook Elementary School is behind the recent public service announcement.

“The one message is I want people to know that gun violence is preventable when you know the signs,” said Nicole Hockley, founder and managing director of Sandy Hook Promise. Her son Dylan, a first-grader, was killed at Sandy Hook. “That’s a big eye opener in itself. People don’t think about gun violence in this way. We think about imminent danger, active shooter drills or lockdowns. This is about prevention.”

On Dec. 14, 2012, 20-year-old Adam Lanza killed his mother, then drove to Sandy Hook Elementary School in Newtown, Conn., where he opened fire, slaying 20 children and six adults before turning the gun on himself. From 2013 through 2015, there were at least 160 more school shootings in the United States, according to data from Everytown for Gun Safety, which tracks school shootings.


Nicole Hockley talks to the media at the New Jersey statehouse in Trenton in 2013. (Julio Cortez/AP)

Sandy Hook Promise has been working to educate people across the United States on gun violence prevention, training about 1.5 million children and adults in less than two years, Hockley told The Post.

The nonprofit released the PSA late last week through the advertising agency BBDO New York. It tells a story about Evan, a boy who is falling in love, while his classmate plans a school shooting.

“Through ‘Evan,’ we sought to show how different your perspective can be when you’re aware of the signs,” Greg Hahn, chief creative officer of BBDO New York, said in a statement. “We’ve been fortunate to work with the inspiring people at Sandy Hook Promise to help parents, students, and teachers better identify these signs.”

Hockley said those signs can include someone showing chronic social isolation (though not everyone who seems withdrawn is likely to commit gun violence); someone obsessed with weapons or firearms; someone exhibiting excessive signs of aggression, or incredibly strong outbursts to what others would see as a minor incident; and someone with extreme behavioral shifts or anti-social behavior.

“We want to point out that this isn’t about one sign,” she said. She said overt threats of violence shown in photos, for example, should be taken seriously. “We’re talking about a buildup, a progression of signs,” she said.

But, Hockley added, “people aren’t trained to recognize them.”

“We wanted to create consumer awareness, plain and simple,” she said about the PSA. “This isn’t a hopeless issue. There are things that you can do in your own community, in your own school to prevent violence.”

The Connecticut Citizens Defense League, a gun rights organization, said in a statement to Fox affiliate WTIC that people have a right to bear arms but should be educated on how to use them.

“While there may be a small number of troubled adolescents in today’s world, many of our youth have a natural curiosity of firearms and would not harm anyone,” the group said in response to the video. “This is why firearms safety and education should be a priority along with proper school security.

“Gun ownership is a constitutionally protected right and we have a duty to make sure that the next generation of legal gun owners are free to exercise those rights.”

Jenn Jacques, an editor for bearingarms.com, criticized the public-service video in an article posted online Monday.

“While I would never begrudge anyone working to end gun violence, I do question the method in which the Sandy Hook Promise is using to do it,” she wrote, adding: “The child in this video obviously has issues that go deeper than access to a tool. Was it bullying, mental health issues or boredom that drove him to attempt to shoot up his school? Let’s say it’s what the child carved into the desk in the video: boredom.”

Jacques suggested that the real issue may be sometimes that parents simply fail to notice what’s going on in the lives of their children.

“The bottom line is, this organization is ultimately calling for ‘sensible state and federal policies’ — also known as sensible gun control, or yet another restriction on our gun rights,” she wrote, referencing Sandy Hook Promise. “Conversely, those interested in protecting gun rights as well as ending gun violence lobby to fix the background check system, reform the criminal justice system, advance the efforts of NSSF’s Project ChildSafe and teach gun safety to grade schoolchildren through programs like Eddie Eagle.

“We don’t need more infringements on the Second Amendment to end gun violence. We just need to fix what’s broken.”

Read more:

Parents need to prepare for school lockdowns, too

There’s a shortage of child psychiatrists, and kids are hurting

It’s true: More people use guns to kill themselves than to kill others