The Disaster

Poul Anderson, Time Patrol (New York, 2006).

(This cover illustrates "The Only Game In Town.")

"A stern chase..." (p. 168) is a chase in which the pursuing ship follows directly in the wake of the pursued.

Having escaped from the Mongol camp, Everard must:

evade Mongol pursuit;
return immediately to rescue the concussed John Sandoval who otherwise will die soon.

However, suddenly there is thunder and lightning and he need not hurry. Above him, Manson Everard has returned on the timecycle. When, later on his world line, Everard tries to arrest Merau Varagan of the Exaltationists, Varagan is rescued by his future self. The Patrol forbids its members to rescue their younger selves:

"Too much danger of a closed causal loop, or of tangling past and future." (p. 170)

 - but Everard has doubled back in time to rescue Sandoval, not himself.

The Patrol exists to prevent one temporal paradox, causality violation, but why do they prohibit the other, circular causality? Sometimes they close a causal circle in order to prevent a causality violation, as in "The Sorrow of Odin the Goth," but otherwise the Danellian ideal seems to be a timeline free from either temporal paradox, which is impossible given the amount of time travel. Patrol activity is impossible without interaction between past and future.

As he escapes, Everard realizes what his older self must be doing and thus what is the disaster that prevented the Mongols from returning home. A sorcerer swooped down, killed their horses and burned their ships. And this closed a causal circle because, with the benefit of hindsight, Mongol and Confucian influence is discernible in some North American tribes. But did Everard and Sandoval need to be confused and captured and Sandoval concussed before the solution was found?