WTM- an interesting position

Some chess tactical problems are just too cool. Here is one with white to move. Many forces are in balance here.

Source: Understanding Chess Tactics by Weterschnik page 19.

addon note: as DG noted the correct move is g4. I find this puzzle to be aesthetically pleasing.
The factors in balance are White desire to put the rook in the backrank is stopped by the queen. The pawn in front of the queen ,the discoverer opens up a discovered attack against the queen as well as interferes with the protection against the back rank mate. Discovered attack in order to be effective normally has the discoverer ( the piece which creates the discovered attack) do something useful such as attacking another piece, delivering a check, blockading.