op-raise w 55, 3bet by unknown, flop QQ8

[Blue Lagoon]

Villain is unknown. What is the standard play here?

PokerRoom 2/4 Hold'em (5 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Preflop: Hero is UTG with 5[img]/images/graemlins/club.gif[/img], 5[img]/images/graemlins/spade.gif[/img].
<font color="#CC3333">Hero raises</font>, <font color="#CC3333">MP 3-bets</font>, <font color="#666666">3 folds</font>, Hero calls.

Flop: (7.50 SB) Q[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/heart.gif[/img], 8[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

Turn: (4.75 BB) 6[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

River: (6.75 BB) 4[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, <font color="#CC3333">MP bets</font>, Hero calls.

Final Pot: 8.75 BB

If it is standard, do you fold if a broadway card hit on the turn or on the river?