Mary Ann Jordan grew up hearing her father's tales of her Irish grandmother, Grace.

In the early 1900s, Grace Jordan was a high-ranking surgical nurse at the University of Michigan, and the stories of her accomplishments made Mary Ann think she could be a nurse too

Grace Jordan wasn't the only family member to stir Mary Ann's interest in nursing. There was also Billy.

Mary Ann was the fourth of the six kids of Philip and Mary Jordan. Billy was the youngest, born with Down syndrome. From early childhood, she connected with him in a unique way, and he was why she wanted to specialize in pediatric nursing.

"She was great with him," recalled their sister, Susan Jordan Morin. "Always very playful and very compassionate. Billy loved her tremendously."

If you asked Mary Ann where she was from, she'd give a classic South Side answer, naming not her neighborhood but her parish, Our Lady of Peace.

She loved swimming, ice skating and softball. She played baseball in the alley, badminton across the back fences. She roller-skated in the basement of the family's three-bedroom bungalow.

It was the kind of childhood that half a century later people look back on and call simpler, innocent, a time when city kids were raised to be independent and unafraid.

But life wasn't all play. Mary Ann had family responsibilities. At age 10, she walked her sister Susan to her first day of kindergarten. When her father was at work and her mother was taking care of the house and Billy, she took Susan along while she ran family errands on 79th Street, where the shopkeepers knew her name.

During the summers she accompanied Billy to nearby Rainbow Beach, splashed with him in the water, hugged him a lot, made him laugh, a boisterous laugh he copied from her.

An impressive and brazen mimic, Mary Ann made everyone around her laugh.

She had a wicked sense of Irish humor.— Susan Jordan Morin, Mary Ann Jordan's sister

Mary Ann brought her Irish humor, her sense of duty and her talent for friendship to nursing school and to the townhouse on East 100th Street.

On a trip to Florida with her classmates not long before she died, she sent a postcard home to report that immediately after their plane landed, they had gone to Mass.

In one photo that captures her impish side, she's tucked in bed with a housemate, the covers pulled to her chin, her hair in a shower cap.

By July of 1966, however, Mary Ann, 20, had moved out of the townhouse and back into the family bungalow. She was home on the night of July 13, when her brother Phil stopped by.

Phil was engaged to one of Mary Ann's classmates, Suzanne Farris, who still lived in the townhouse, and Suzanne was with him that evening.

Come spend the night at the townhouse, Suzanne suggested to Mary Ann. They could talk about the wedding. And so, shortly after 12:15, Mary Ann and Suzanne climbed the stairs to Suzanne's bedroom. Richard Speck was waiting.

When Susan Jordan Morin, who now lives in Chicago's suburbs, thinks back to the day her family heard the news, her mind lands on a vivid memory of Billy. Billy, the spirited boy who rarely spoke more than two words at a time, blurted three: "Mary Ann's dead!"

Billy died at 42, with Susan as his caretaker.

Jordan Morin, who was 15 when Mary Ann died, has never before spoken publicly about her sister's death, and she doesn't talk easily about it now. Only one of her siblings, a brother, is still alive. Her brother Phil, who lost both his sister and his fiancee on that July night, died at 64.

For her to discuss an event she calls "still unbelievable" is an act of faith, one she commits only because she'd like the world to pause and think about Mary Ann and her friends.

"Let people know who they were," she said. "What wonderful people they were."

Here's an image she holds on to, one her father captured on a Super 8 movie camera:

A sunny Easter morning. Susan is 3. Mary Ann is 8. They're walking home from church, dressed in matching blue coats and hats and black patent leather shoes, each clutching an Easter basket. They are young and together and happy