A Narrow Escape

Sometimes in Chess, one single move has the power to change a lost position into a won one. The position below is a primary example: Black is two pawns behind, plus his Queen and Knight are both attacked by the powerful placed White Rook at c5; it appears that Black will lose the knight. So, Black should resign, right? wrong, Black has a fantastic resource at his disposal that puts White in big trouble, 1...Ng4!!. Now White can forget about winning, at the brink of resignation, the best he can come up with is an ingenious draw by perpetual check.