Harry had to work, at the last minute.
"They fly her lots of places, on short notice," John said, again.
Sherlock had always been suspicious: neither the story itself nor John's responses were reliable indices, because John would always choose credulity over disappointment where Harry was concerned. But Sherlock would have to re-evaluate, now. Sherlock had limited data to work with on Harry, but none of it suggested that she would choose to give up one of her weekends with her son.
Peter arrived right before noon, coming up the stairs hand-in-hand with John, and his eyes grew wide as he took in Sherlock's latest experiment. "Is that a real brain?" he asked. "Can I touch it?"
John had begged him to be nice, so Sherlock smiled. "Sure, let's –"
"No, we're going out, actually," John said hurriedly. "Where, um, is there anywhere, Peter…"
Peter had been trying to pull away from John's hand, but now he turned back to his uncle, eyes shining. "Trampoline park!" he crowed. "Mum won't take me, and Mama's too busy."
"Yeah, okay," John replied. He already sounded exhausted.
"I'll come along," said Sherlock. "Another adult will be helpful."
"Another adult," John repeated. Sherlock couldn't decide if John looked defeated or relieved.
"Come on," Sherlock said, taking Peter's hand. "Let's go see how high you can bounce."