Straight on paired board

Opp is 19/7/1.7, no real other reads.

How is this line? Fold the flop to the re-raise? What do I do on the river?

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $0.10/$0.25
9 players
Converter

Stack sizes:
UTG: $25.35
UTG+1: $22.30
MP1: $123.55
MP2: $21.90
MP3: $11.30
CO: $11.60
Button: $25.25
SB: $26.55
Hero: $24.05

Pre-flop: (9 players) Hero is BB with 8 :heart: 7 :diamond:
3 folds, MP2 calls, 2 folds, Button calls, SB folds, Hero checks.

Flop: 6 :heart: 5 :club: K :diamond: ($0.85, 3 players)
Hero checks, MP2 checks, Button bets $0.75, Hero calls, MP2 raises to $2.25, Button folds, Hero calls.

Turn: 6 :diamond: ($6.1, 2 players)
Hero checks, MP2 checks.

River: 9 :club: ($6.1, 2 players)
Hero bets $5, MP2 raises all-in $19.4, Hero ????

If ever a boat (or quads) has seemed obvious it's in this hand. I wonder if a clever player with the same hand as you might check/raise that flop? It seems highly unlikely.

The slightly baffling part is his check behind on the turn. You've already called two bets and raises on the flop so you're probably drawing - if so, another bet here is surely the way forward for him, something nice and small that you'll be priced in to call. Also, if he is (semi-) bluffing, then he's likely to fire another barrel here - he could simply be trying to induce a bluff on your part but it all feels too sophisticated for 25NL. He might just be doing the typical fish thing of slowing right down when he hits his monster.

Considering the size of the bet you're having to call, I think you can fold this fairly easily. He hasn't given you any reason not to believe him.

the reason he might have slowed down on the turn is because his hand is now "safe". it's unbeatable so he thinks he can afford to slowplay. a straight can't draw out on him. i used to have that mentally when i was starting out.

Fold flop, fold to river push. And include number of hands with your stats :)