facing unexpected donk bet from TAG with fish sandwich

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SB is a tag (16.5/12/3/2+2) that I have a fair amount of history with. He respects my play and he doesn't like to play against me because I 3-bet him like mad. He used to avoid me, but that isn't the case anymore. He normally does not play 400 NL, but UTG is an exceptionally weak player. I might expect SB to be a little conservative, but not nitty.

UTG is 66/5/1.4 over 800 hands and very weak. He tends to check/raise strong hands, and will play them aggressively. He can be calling the flop with a fairly wide range, but not total air. I figure I am ahead of his range though - I think it's likely (though not definite) that he would raise a monster. He probably wouldn't raise a combo draw, but again he is unpredictable.

What should I do on the flop after this unexpected donk bet? What's a good plan for the rest of the hand?

No Limit Holdem Ring game
Blinds: $2/$4
5 players
Converter

Stack sizes:
UTG: $1.228.00
CO: $879.00
Hero: $400.00
SB: $400.00
BB: $432.60

Pre-flop: (5 players) Hero is Button with K[img]/images/graemlins/club.gif[/img] Q[img]/images/graemlins/spade.gif[/img]
UTG calls, CO folds, <font color="#cc0000">Hero raises to $20</font>, SB calls, BB folds, UTG calls.

Flop: T[img]/images/graemlins/spade.gif[/img] Q[img]/images/graemlins/diamond.gif[/img] 9[img]/images/graemlins/club.gif[/img] ($64, 3 players)
<font color="#cc0000">SB bets $44</font>, UTG calls, <font color="green">Hero?</font>