In the Mordred museum on the second floor.
It is under the bed in the place where you have to pay with the golden coin.
in the upstairs of the museum.
In the museum.(the top floor)
catch the mouse
get the missing page of mordreds jornal wich is under mordreds bed
there are haystacks push them then get the key
near the mill underneithe the two hay barrels
Mordred's lab is in Astroknights Island and in between the hay.
you push through
Chase it out of the cave/Mordreds lab and then set the mouse free.
The Missing Journal Page tells you where you're going, but you need a spaceship to get there. The saucer Excalibur is crashed out in the mud past the Mill. (see related questions)
just go to coordinates x=11 y=81