Flop nut straight, River Nut Flush -- what to do?

Loose 15-30 game, UTG (LAG) open limps, MP2 (very loose PF, plays well PF), CO raises (weak, could raise with anything, usually follows through on PF raise with automatic bet on flop).

Hero calls from SB with A [img]/images/graemlins/heart.gif[/img]10 [img]/images/graemlins/heart.gif[/img]
BB (regular, good player) calls
UTG calls
MP2 suddenly 3-bets. (He's been doing this all night to "build a pot", raise signifies nothing)
CO calls 3-bet, Hero, BB, UTG all call.

Flop: K [img]/images/graemlins/heart.gif[/img]J [img]/images/graemlins/heart.gif[/img]Q [img]/images/graemlins/diamond.gif[/img]

Hero checks. Checked all around (ugh).

Turn: J [img]/images/graemlins/spade.gif[/img]

Hero bets: BB folds, UTG raises, MP2 folds, CO folds, Hero thinks about it, then just calls hoping for some action on the river (Hero and UTG have overs buttons so betting goes up to 30-60).

River: 6 [img]/images/graemlins/heart.gif[/img]

Hero checks.

UTG puts in an overs bet.

What should Hero do?