Check
Can you find it?
Find 89... Rb8+. What is the idea?
Drag the move on the board, or type the move if you already see it.
Need a hint?
The answer is a check idea. Start by checking forcing moves.
Solution: Rb8+ — Rb8+ is a forcing move. It keeps initiative by using check pressure, so the defender has to respond before solving the larger king-safety problem.