A very strange land : the first adventure in the Merryvale series

Lorelei and Sarah receive a mysterious notice in the mail: Merryvale stables invites you to a most special schooling show--October 32nd--don't bring your nag, horses will be provided. The show will be held in spite of the fog. Take freeway north past forest lake. Exit at Merryvale at the highest rate of speed you can manage. When is October 32nd? How do they know there will be fog? And why can't they take their own horses? Find the answers ... and many more questions ... in this the first of three in the Merryvale series. Best friends Lorelei and Sarah receive a mysterious invitation to a schooling show being held at Merryvale Stables. The weird thing is that the horses will be provided, and it's to be held on October 32nd, in a place that doesn't seem to exist