8
7
6
5
4
3
2
a1
b
c
d
e
f
g
h
Step 1 / 2
The black king on c8 has its own rook on d8 and pawn on d7 blocking two escape squares. Your bishop on f4 already rakes b8. Bring the other bishop to a6 with check and the two diagonals cover everything that's left.