Agents, knowledge and backwards causation

Although many philosophers think backwards causation possible, puzzles arise when we consider worlds containing both backwards causal chains and agents capable of intervening in, and initiating, such chains. In these worlds, agents have the power to bilk, that is, the power to prevent an event from occurring which, had it occurred, would have been the cause of an earlier event. I argue, appealing to Max Blacks example and one other, that this power is absurd and hence that there are no worlds containing both agents and manipulable backwards causal chains.