Is This an Overbet or Bluff? What would you do?

[Chomper4]

Now I know I probably made a mistake in this hand on the flop, but I just want to know what you would do on the river to the villains push. The villain hadn't shown any crazy hands and hasn't made a bet this big since I had sat down. What would you put the villain on and what would you do?

PokerStars No-Limit Hold'em, $2 BB (7 handed) internettexasholdem.com

BB ($104.60)
UTG ($204.05)
MP1 ($227.90)
MP2 ($157.20)
CO ($197)
Hero ($209.75)
SB ($239.80)

Preflop: Hero is Button with J[img]/images/graemlins/spade.gif[/img], Q[img]/images/graemlins/spade.gif[/img].
UTG calls $2, <font color="#666666">1 fold</font>, <font color="#CC3333">MP2 raises to $8</font>, <font color="#666666">1 fold</font>, Hero calls $8, <font color="#666666">1 fold</font>, BB calls $6, UTG calls $6.

Flop: ($33) 9[img]/images/graemlins/club.gif[/img], 8[img]/images/graemlins/club.gif[/img], Q[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
BB checks, UTG checks, <font color="#CC3333">MP2 bets $18</font>, Hero calls $18, BB calls $18, UTG folds.

Turn: ($87) K[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
BB checks, MP2 checks, Hero checks.

River: ($87) K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
<font color="#CC3333">BB bets $78.6 (All-In)</font>, MP2 folds, Hero??