A group of loosely connected strangers visiting the remains of an amphitheater are shunted back and forth through time, eventually alighting in 1865, where they end up having to battle with other, less-than-friendly time travellers.
Entertaining enough read, but some things were left inadequately explained (surprising considering the length of the book), and I didn't feel the ending really, well ... ended.
Okay, but I've enjoyed other work by Clark far more.