17 down
Second
person
on
computer
is
chasing
kitty
(6)
Second person on computer is chasing kitty (6)
hints
0
checks
0
hints
The definition is at the end of the clue.
How the clue works
The definition is chasing kitty — a mouser being a cat that hunts mice. The wordplay stitches together MO (a "second" as in a moment) and USER (a person on a computer).