Sometimes a solution to a problem cannot be deduced by a purely sequential reasoning process- a leap of imagination is required. It seems likely that White's queen will be involved, because at the moment she is not using her full powers, but how exactly? 1 Kd6! This certainly brings the queen into the game, because this creates a threat of 2 Qb7 mate, but otherwise it appears to be one of the most unlikely moves on the board. Not only does it allow Black's king to flee to b4, it also permites Black's rook to deliver check on either g6 or d3. However both these checks block the h7-bishop's attack on b1, allowing White to give mate by discovery 1...Rd3+ 2 Bd5 mate or 1...Rg6+ 2 Be6 mate. The only other  move to meet the threat is 1...Kb4, but this leads to the thrid mate by discovery after 2 Kxc6.