In the 2150's, a scientist discovers time is actually fluid; past, present, and future all exist at the same time. What he doesn't know, is if the current timeline can change when something is changed in the past. The U.S. government wants him to find out. The theme being to make right what once went wrong.
Wounded Knee 1890
Titanic in 1912
Anne Frank in 1940
JFK and the assassination in 1963
Challenger in 1986