In Time Agents the players are time agents. These special operatives are sent back in time to correct problems in the timestream. Problems are identified using the Codex, a computer system which operates outside the timestream. The coders describe significant events to the Codex and the Codex looks for changes. If events in the past are changed, it can change the future. The TimeAgents are sent back in time to correct the timestream and maintain the status quo from nefarious influences.
Of course, things aren't always easy -- people can't be sent back in time, only their psyches. When they arrive they inhabit the bodies of nearby animals. They must use their animal bodies and human intelligence to accomplish their goals