Don't be fooled into thinking that there's only 1 mouse - you probably have at least 2 and if you don't get rid of them quickly they can grow exponentially (that's mice numbers that is).
Traps are best - the sonic pest repellers don't work very well (my guess is that the mice will put up with the noise if there's a readily available food supply) - don't just pop a piece of cheese into the traps as they will just nick the cheese without setting off the trap but force the cheese into the hole so that the mouse has to use a bit of force to get the cheese out thereby setting off the trap.
The traps sometimes dont always kill the mouse outright, as I trapped a mouse by it's hind legs and had the unpleasant task of battering it's brains out - my wife said she would have battered it's brains out as well given half the chance, as it chewed a hole in her designer leather handbag

Anyway hope you get rid of them quickly as they are destructive little buggers
