There's a sac in the air

From a game last night - black to play.

Try to solve it -- the comments below are hidden...( show | hide).

The game went:
... Nxf2
Kxf2 Be3+
Kf1 Qg3
Nd3 Bg6
...and White didn't see that Bc1 holds

Strelka sees:
... Nxf2
Kxf2 Bxf3
gxf3 Be3+
Kg2 Nh5
f4 Nxf4+
Kh1 Nxh3
Nd3 Qg3
...and black ends up "+4"