"Oh, John," said Mycroft. "Don't tell me you believed that nonsense about the secret, tragic, murderous, and hitherto entirely unknown youngest Holmes sibling."
"Pardon?"
"It was a metaphor. A little 'joke' from our friends across the Channel." Mycroft sighed at John's continued bewilderment. "Her name wasn't a coincidence, either."
"Eurus?"
"Hardly," Mycroft sniffed. "Euros: the East Wind, or the economic power of the entire European Union?"
"What!?"
"They wanted to send me — the British government, that is — a message."
John said, comprehension dawning: "You can't mean this was really about..."
"Brexit," said Mycroft grimly.