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.
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
“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.