"En passant" chess puzzle

Futility Closet posts some very interesting chess puzzles, and the one above is one of best I have seen.

White plays B-g2+.  Black responds with pawn to d5, which (he says) blocks the check and uncovers a checkmate by the black bishop at c8.   White responds that the black pawn never got to/can't go to d5, because the white pawn takes it "en passant" at d6. 

More at the link (puzzle from Heinrich Fraenkel, Adventure in Chess, 1951.)