Arrival is episode 1 of Mirror Mirror Series 2 and episode 21 overall.
The mirror appears in an attic in the country at Limerick House in a town called Greyton. Daniel McFarlane is on his way to meet his father, stepbrother Fergus and half-sister Mandy for the first time. The reception that he receives is less than welcoming. After Mandy gets upsets and runs to the attic, Daniel follows her. In the reflection of the mirror he sees a girl, Constance de Lutrelle. Mandy gets in the way and they accidentally go through to the goldfields in 1867.