5-10 NL, CRed all-in on flop with middle pair, nut flush draw

[PokerNeophyte]

5-10 NL, hero on button has about $550, villain in BB has hero covered.

Dealt to hero:
A [img]/images/graemlins/heart.gif[/img]9 [img]/images/graemlins/diamond.gif[/img]

MP raises to 35, one player calls before hero, hero calls, villain calls, four players to flop.

Flop:
K [img]/images/graemlins/heart.gif[/img]9 [img]/images/graemlins/heart.gif[/img]3 [img]/images/graemlins/heart.gif[/img]

Checked around to hero. Hero bets 140, villain check-raises all in. Folded back to hero.

Hero?