Sherlock Season 4: 18 Easter Eggs & References From 'The Lying Detective'
2. There's An East Wind Coming
Eurus also explains that her name means "east wind." This will be of importance to Sherlock fans as it is a concept heavily referenced in season three finale His Last Vow.
In that episode, we found out that the east wind was a story Mycroft told Sherlock to scare him when they were kids. It was about the fabled east wind which would one day come for Sherlock. Now it looks like the day is coming very soon.
The east wind idea comes from Doyle story His Last Bow. Set shortly before WW1, Holmes speaks of an oncoming east wind that will damage the country but ultimately leave it a stronger place.