1.Rd1+ Ke6

Has to be the first moves because:

1.Bxc6+ would work if the king has to take but it doesn't
1.Bc4+ is just suicide
Anything else and black get perpetual check

But I cannot see where it is heading

2.Bc4+ otherwise white gets perpetualed
2...d5
Now:
3.bxc8=B+ Qxc8
4.exd6+ e.p. Kd7 is no good

3.exd6+ e.p. would work but black plays Kd7 check! If it wasn't check then b8=N would be mate

I can't see it