Daily Puzzle 20180331

White to move, blocking (Step 5)

answer

Qg7+ Kf1, Qa1+ Qe1, Qa6+ a) Kf2, Qa2+ ..., Qg2# b) Kg1, Qg7+ ..., Qg2#
or
​Qa1+ Qf1, Qg7+ Kf2, Qg3#