Where do I fold this TPTK?

[kem]

Usual party $0.50/$1.00 table. Is this a no-brainer fold when the flop is capped? It sure felt like I was up against a set, but I guess I was a little slow and didn't fully accept it until the turn...

Party Poker 0.50/1 Hold'em (9 handed)

Preflop: Hero is MP1 with A[img]/images/graemlins/spade.gif[/img], K[img]/images/graemlins/diamond.gif[/img].
UTG folds, UTG+1 calls, <font color="CC3333">Hero raises</font>, MP2 folds, MP3 calls, CO folds, Button calls, SB calls, BB calls, UTG+1 calls.

Flop: (12 SB) 6[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/diamond.gif[/img] <font color="blue">(6 players)</font>
SB checks, BB checks, UTG+1 checks, <font color="CC3333">Hero bets</font>, <font color="CC3333">MP3 raises</font>, <font color="CC3333">Button 3-bets</font>, SB folds, BB folds, <font color="CC3333">UTG+1 caps</font>, Hero calls, MP3 calls, Button calls.

Turn: (14 BB) 5[img]/images/graemlins/heart.gif[/img] <font color="blue">(4 players)</font>
<font color="CC3333">UTG+1 bets</font>, Hero calls, MP3 calls, <font color="CC3333">Button raises</font>, <font color="CC3333">UTG+1 3-bets</font>, Hero folds, MP3 calls, Button calls.

River: (24 BB) K[img]/images/graemlins/club.gif[/img] <font color="blue">(3 players)</font>
UTG+1 checks, MP3 checks, Button checks.

Final Pot: 24 BB
<font color="green">Main Pot: 24 BB, between UTG+1, MP3 and Button.</font> &gt; <font color="white">Pot won by UTG+1 (24 BB).</font>

Results in white below: <font color="white">
UTG+1 shows 9c 9s (full house, nines full of kings).
MP3 shows Th 8h (one pair, kings).
Button shows 6d 6s (full house, sixes full of kings).
Outcome: UTG+1 wins 24 BB. </font>