Tsume Othello #5622101 (empty 10)
To move: Black — find the best move
a
b
c
d
e
f
g
h
1
2
3
4
5
6
7
8
33 21
Why this move works
The answer is a5. Read to the end, it wins by a final +8, and is 4 discs better than the next-best.
The biggest immediate flip is b3 (4 discs), but it is not best. Judging by the final count is the path to the right move.