Here’s another Binary Homeworlds puzzle, inspired by Raymond Smullyan’s The Chess Mysteries of Sherlock Holmes.

For details of how I created the puzzle, how I created the image (thanks to Sleafar on Puzzling StackExchange!), and where to get your own physical set of Homeworlds pieces, see the first post in this series.

The puzzle

Holmes and Watson happened to be passing by the table just as Lee made his move in a game of Homeworlds. The position after Lee’s move was:

Lee (0,r3g1) y3b2-r1
Ray (1,y3b2) -y2y1b2
DS1 (g2) -b3b3y3
DS2 (b3) -r1g1y2
DS3 (b1) y1y1-b1b1
DS4 (g1) -y2r1

(The stash contained r3r3r2r2r2 g3g3g3g2g2.)

“Interesting move, Lee,” said Watson. “You know, if you had moved your blue ship just now, you would have put Ray in check.”

“Yes,” replied Lee; “but if I’d done that, then Ray surely would have responded by catastropheing half of my home star!”

What was Lee’s last move?

For the solution, see the discussion of this puzzle on BoardGameGeek.