At Different Times

Poul Anderson, The Corridors Of Time (London, 1968).

Lockridge spoke to Brann of the Rangers in the fortieth century;
consequently, Brann attacked Storm's Wardens in a time corridor that they had built from the twentieth century and captured Storm herself in 1827 BC;
but Lockridge led Wardens from 1535 AD to 1827 BC;
these Wardens freed Storm and captured Brann;
the Wardens now propose to send Lockridge to speak to Brann in the fortieth century, thus leading him through apparent victory into a trap.

What if Lockridge refuses? If he were the sort of person who would refuse at this stage, then this sequence of events would not have started and he would not have to refuse.

Lockridge has arrived in the fortieth century;
Storm is absent from the fortieth century, having departed to the twentieth century (and from then to 1827 BC);
Brann is in his headquarters, not yet having spoken to Lockridge or attacked Wardens in a time corridor;
the Warden Hu informs Lockridge of intelligence to the effect that he, Lockridge, having spoken to Brann will be neither killed nor detained but will escape into a time corridor;
thus, Hu receives some intelligence from his near future even though corridor guardians prevent either Wardens or Rangers from traveling into later periods;
however, Hu merely hopes that Lockridge will rejoin him in the Warden country within a month;
because of the uncertainty of the emergence time from a gate, there is no single present moment to which time travelers can return.

It is clear that, even without time travel, there is a lot of intelligence and counterintelligence activity. The Wardens can spare Lockridge only a single night before sending him to Brann because there are too many spies about. When one of the sides thinks that it is strong enough, it will launch the onslaught.