Tess is a geologist (because, of course, geologists control the time travel of the giant
ancient machines) and a member of the Daughters of Harriet (Senator Harriet Tubman, that is,
from 19th-century Mississippi). On the surface, the Daughters are time travel scholars, but
in reality, Tess and her fellow Daughters are fighting a pitched changewar for women’s
rights against the oppressors known as the Comstockers. One more thing: While she’s at
it,Tess also hopes to also save the souls of her teenaged self and her underground feminist
punk friends in the 1990s, with a particular focus on their vigilante killing spree and young
Beth’s abortion.
— Michael Main
All five Machines had limitations, but the hardest to surmount was what travelers call
the Long Four Years. Wormholes only opened for people who remained within twenty
kilometers of a Machine for at least 1,680 days.