Attack on the Castled King

Certain positional features should set off tactical buzzers in your mind. One of these is a king with few or no defensive pieces around him. The king doesn't like to be left alone and can often be dethroned rapidly if none of his friends are hanging out with him.

In the following game white left the king nearly bare and enough tactical weakness for black to come crashing through.

 Here is the remainder of the game as a puzzle:

The puzzle variation is how the game played out. If you have questions regarding alternative moves for white, please see the move list first.