Billy Delahunt boarded a Red Line train with his mom at Boston’s Downtown Crossing station heading towards Harvard Square in Cambridge for his piano lesson and then afterwards, she promised, to shop for a new skateboard. Because their train car was almost empty, he and his mom had no problem finding seats.

Billy loved to observe the other passengers. Sitting across from him, for example, was an Asian lady, her long dark hair carefully brushed and all in place, tidily dressed for work in matching clothes, intently checking her BlackBerry. A young woman standing near a door was gripping a pole with one hand and the handle of a baby stroller with the other. Also standing near the same door was a grey-haired man in a blue blazer and red tie, white trousers, and brown loafers. At the far end of Billy’s train car, a young man chatted with two women, all three of them probably students based on their ages, casual dress and backpacks. The women laughed at something that the man said, which Billy was unable to overhear above the basso profundorumble of the train’s steel wheels and the creaks and shrieks from the train car’s undercarriage as it braked and swayed around turns, noises that were amplified in the reverberant Red Line tunnel.

Billy stared unblinkingly at his fellow Red Line passengers and being only eleven, he did not glance away even when one of them caught him staring. However, their faces revealed little beyond the obvious external clues; they were non-threatening, non-welcoming, and frustratingly for Billy’s research purposes, blandly non-expressive.

Suddenly shattering the spell and causing Billy almost to  jump out of his seat, the neatly-dressed Asian woman right across from him screamed, “Oh my God!”

She lurched sideways and stared transfixed at the empty space beside her and exclaimed again, “Oh my God!” and then, “Robbie! You’ve come back to me! Is it really you?” She began to sob, causing her eye make-up to run, which smeared glistening smudges on her formerly immaculate cheeks. “Oh my God!” she repeated. “I can’t believe it!”

But Billy saw no-one sitting next to her, nor standing in front of her. There was no-one there, no “Robbie” nor anyone else.

He checked whether the woman might be communicating with someone – her Robbie – through a Bluetooth headset hanging off one of her ears, perhaps hidden under her dark hair, but her ears were ornamented only by small gold hoop earrings. Her hand clenched as if it were taking hold of something. “I’ve missed you so much!” she said, and then paused, looking at the space next to her, seeming to listen.

As their train approached the Central Square station in Cambridge, the woman stood up from her seat and pleaded, “Come with me, Robbie. Promise that you’ll stay with me!”

The grey-haired man and the baby-stroller woman sidled aside to give her extra space at the train car door. They let her get out first, and then followed several paces behind. After the door slid shut, she turned back towards the train car. She looked surprised, and then distraught, and cried out, “Where are you? Robbie! You promised you’d stay with me!” Billy could hear her calling frantically, as the train began to move, “Will I see you again?”

Billy’s mom was flipping through a free Metro newspaper that someone had left on a nearby seat. “Did you see the woman crying?” Billy asked.

“Yes. She was very emotional.”

“Did you hear what she said?”

“Not really,” Billy’s mom said, “I was reading the paper.”

“She was talking to someone.”

“So?”

“But she was alone!”

“Maybe on her cellphone.”

“No cellphone. No Bluetooth. I checked.”

“Sometimes people just talk to themselves.”

“Well I thought it was weird.”

“You’re weird yourself,” his mom said and added, as the train slowed to enter the Harvard Square station, “This is our stop.”

Once they were on the platform, Billy repeated to his mom, “She was really sad when she got off the train.” When his mom did not respond, Billy pointed to an official MBTA sign attached to the red-tiled station wall, “See Something? Say Something!”

“That’s for security. It’s not about ladies on the train who were crying.”

“I want to report it.”

They approached a man wearing an MBTA uniform, including the official logo, a black T inside a silver circle, stitched on the right shoulder of his jacket. “My son wants to make a report,” Billy’s mom said.

The MBTA man listened attentively as Billy described what he saw. He asked for all the details that Billy could remember and took notes as Billy talked. He thanked Billy for his report and assured him that he would pass it along to the proper authorities.

“Satisfied now?” his mom asked, once they were on their way again. They were going to be late for Billy’s piano lesson with Mrs. Fiona Lewis, who was a stickler for starting on time, so his mom hustled him to keep up with her as they climbed the steps out of the station to street level in Harvard Square.

After Billy’s piano lesson, he texted his friends about the lady he saw crying on the Red Line, about how she was talking with someone who wasn’t there, and about how the MBTA man in the Harvard Square station seemed really interested when Billy reported what he saw.

One of his friends responded, “Sweet!” and another replied, “Woo! Maybe she was talking to a ghost!”