I must have read his in the nineties. I think it was a series of books. The first book starts off with a woman in a cabin in a modern day american desert. I think a biker dude turns up and then a wizard appears with baby and transports them to a parallel medieval world. The woman joins the city watch protecting the baby and the biker dude becomes apprentice to the wizard.

I remember once scene where the biker dude casts a spell to change his appearance to a dung beetle to sneak past some guards thinking it would be inconspicuous, but the locals had never seen a dung beetle before.

The book was written in English.

Does it ring any bells with anyone?