Dotty nodded, squeezing Johan’s arm. “We’ve been married since 1958. Sixty-three years.”

Jess wasn’t an emotional person by nature; she adored her daughter and grandparents to the stars and back, but she wasn’t one to cry at commercials and was the only person in her life who could listen to Adele’s “Someone Like You” without weeping. But the moment caught her like a hook, and she felt a swell of emotion rise, salty, in her throat.

Through this deep, sweeping emotional moment—as she struggled to balance reverence and enthusiasm—Jess noticed Johan’s outfit. He was wearing a blazer and dress pants, but beneath the coat was a T-shirt, not a dress shirt. On it was a benzene ring with iron atoms replacing the carbon, and beneath it the words FERROUS WHEEL.

“I realize this is a fancy affair, but I wore it for River,” Johan said, noticing her amusement. “He loves terrible science puns.”

“Does he?” Jess asked, looking at the man in question.

Mr. Fuchs cleared his throat, raising a finger. “What did Gregor Mendel say when he discovered genetics?” He waited a beat and then sang, “Whoopea!”

It was corny, but his delivery was fantastic. Besides, he might have been the smallest, sweetest old man Jess had ever seen. She would laugh at any joke he told for the rest of time.

“Very clever,” River agreed, eyes twinkling. “What is the fastest way to determine the sex of a chromosome?” he asked. “Pull down its genes.”

Everyone groaned.

“Potassium and oxygen went on a date,” Johan said, grinning as their game started rolling. “It went OK.”

Dotty groaned just as Jess said, “Okay, that one is cute.”

“I wish I was adenine,” River said, and winked down at her. “Then I could get paired up with U.”

Everyone Awww-ed audibly, and then three pairs of eyes turned to Jess with anticipation. After a beat, it sank in: she was up to bat. “Um,” she said, digging around the dusty reaches of her brain for a science joke. “Okay, anyone know any good jokes about sodium?” She scanned their faces, grinning. “Or Na?”

Mr. and Mrs. Fuchs looked at each other. “I don’t think I do,” Dotty said, frowning. “Do you know any, darling?”

“No, it’s—” Jess stammered.

“I don’t,” Johan said. “Well, let’s see now. That is a rather specific request. Sodium. Sodium jokes…”

“No,” she said, “the joke is—” She gave up as they continued to confer, mumbling to each other.

“Sorry, dear,” Dotty said. “No sodium jokes, but I am so delighted to meet you.” She smiled up at River. “It’s good to see you, darling. You take care of her, okay?”

“I will.” He bent, kissing her cheek again. Jess and River watched them walk off together, holding hands.

Silence settled over the two of them, and Jess laughed out a quiet “Wow.”

“Only the best jokes require explanation immediately afterward,” he said, eyes dancing at her.

“They do call me the Party Cooler.”

“Do they?” he asked.