03 Sep 12
I had to look this one up. Tough problem...
Here's the sol if anyone wants to give up.
Add bRb7, bNc8d7; retract -1. Qd8-c7 Nf8xNd7 -2. Ne5-d7 Rd7xRb7 -3. Rc7-b7 Rb7-a7 -4. Nf3-e5 Qa7-a8 -5. Ne5-f3 Ka8-b8 -6. Nf3-e5 Qb8-a7 -7. Ba7-b6 Nb6-c8 -8. Rc8-c7 Nc4-b6 -9. Bb6-a7 Ra7-b7 -10. Bc7-b6 Rb7-b5 -11. Ne5-f3 b5-b4 -12. Nf3-e5 b6-b5 -13. b5xQa6. Bf8 was captured on b4.