MI6 has discovered a recently activated Soviet Sleeper Cell operating in London, they've given the task to you to determine where, when, and how they will strike.
You come across the location of their last known meeting, the trail is several hours cold, but they've left a chessboard out looking like this.
A book is open to a historical game: Spassky v. Bronstein, Leningrad, 1960 complete with movelist and analysis. (For your convenience, the move list follows):
23.Qe4+ Kh8 1-0
You can tell it's the game for which the end position is on the board.
In the trash you find a crumpled index card, one side covered with mysterious writing.
S1R23R23S9s2p22 S9R23 S10S1S18P20
The method of encyphering is one->many, in database terms, however each symbol in the ciphertext decodes to exactly one symbol in plaintext, depending on the key used.
After several hours of investigation, you receive a call from your superiors.
Be careful, we have reason to believe this group has acquired a dangerous spore-based biological agent they may use in this attack.