Overcalling a big all-in on the flop with the nut flush draw?

[LaggyLou]

10+1, about the fifth or sixth hand in, no reads

Party Poker No-Limit Hold'em Tourney, Big Blind is t15 (10 handed) converter

UTG+1 (t695)
UTG+2 (t995)
Hero (t950)
MP2 (t810)
MP3 (t730)
CO (t725)
Button (t705)
SB (t645)
BB (t695)
UTG (t1050)

Preflop: Hero is MP1 with A[img]/images/graemlins/diamond.gif[/img], 8[img]/images/graemlins/diamond.gif[/img].
UTG calls t15, UTG+1 calls t15, UTG+2 calls t15, Hero calls t15, MP2 calls t15, MP3 calls t15, <font color="#666666">1 fold</font>, Button calls t15, SB completes, BB checks.

Flop: (t135) 4[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(9 players)</font>
SB checks, BB checks, UTG checks, UTG+1 checks, <font color="#CC3333">UTG+2 bets t80</font>, Hero calls t80, MP2 calls t80, MP3 folds, <font color="#CC3333">Button raises to t690 (All-In)</font>, SB folds, BB folds, UTG folds, UTG+1 folds, <font color="#CC3333">UTG+2 calls t610</font>, Hero.....??????