The key, 1.Ra6, threatens 2.Rd6+ Kxe5 3.Rxd4. Black can defend by moving his bishop, leaving a flight square at f5.
Two defences prevent the rook from checking at h7, freeing the h6 rook.
1...Bh7 2.Rhxe6 threat 3.Rad6 and 1...Bh3 2.Rh8 threat 3.Rd8. Defences on the g-file again prevent a check, freeing the knight to guard e5.
1...Bg6 2.Sgf3 threat 3.Rd6 and 1...Bg4 2.Sf7 threat 3.Rd6. 1...Be4 interferes with the d4 rook, allowing 2.f4 threat 3.Rd6.
Finally 1...Bxd3 prevents the pawn from vacating c4, freeing the d2 knight 2.Sdf3 threat 3.Rd6.
A clear-cut theme with no distracting by-play, the work of a master composer.