！
And now, enter Beth from stage left!
Literal
There, Beth stage-left [from-より] appearance!
Theater-stage announcement register. そこで here is the temporal 'at that point, then' sense (not the locative 'there'). ベス is a proper noun (a character named Beth). 下手 read しもて means 'stage left' in Japanese theater — distinct from the same kanji read へた 'unskilled.' より is the literary/formal version of から 'from.' 登場 'appearance, entrance (on stage)' is a theatrical verbal noun; the sentence ends on it as a noun fragment with an implicit 'here comes!'