The two dated briefly in December 2012, but were just friends in August 2013 when they boarded a train for Kennedy International Airport, where Ms. Watson had a one-way ticket to Australia and dreams of starting a new life there after graduating from the University of Tennessee in Knoxville with a degree in microbiology. She was a four-year athlete there on the swimming and diving team, and competed in the 2008 and 2012 Olympic Trials in swimming.

“I had a couple of interviews set up in Sydney, but I was also ready to work in a bar or on a farm there if I had to,” said Ms. Watson, a daughter of Karen Watson and Mr. Watson of Memphis. (Her father is a lawyer there and her mother an executive with a charitable foundation.)

“I was caught up in the adventure of it all,” Ms. Watson said.

But Ms. Watson, who had asked Mr. Madubuonwu upon arrival in New York to help her navigate the city’s subway system to the airport as he was now living in Manhattan, soon found herself in an unexpected adventure. The travel agency she used to book her flight had printed the wrong name — “Brooke Wa” — on her ticket. With the last four letters of her surname also missing in the airline’s database, she was not allowed to board the plane.

“I was sort of freaking out, and to make matters worse, the flight was delayed several times,” Ms. Watson said. “I called my mom, who proposed that I come back to Memphis. But that really wasn’t an option.”