Although I have not finished Fathom Five, I am still thinking about the third book to feature Peter and Rosemary. I’m envisioning a historical. Peter and Rosemary are visiting Theo’s basement apartment in downtown Toronto when the floor collapses and they fall through into an underground river. Walking out, they emerge onto the University of Toronto grounds, and discover that they have walked out into Toronto, circa 1884.
I used to live just south of the University of Toronto, and I’m fairly sure that Taddle Creek flowed beneath our house. It used to run from near Bathurst and Davenport all the way to Lake Ontario before the City of Toronto converted it to a storm sewer and buried it.
I have a fair amount of historical research ahead of me to make this story work, but I’m looking forward to it. Did you know that Taddle Creek was last seen on the surface in 1884? It ran through the University of Toronto grounds until it became so contaminated with runoff from Yorkville that the University finally closed it off. I got this information from the Lost Rivers Website, which speaks of returning Taddle Creek to the surface. Sadly, their website appears to be inactive.