Nicholas Van Rijn, Detective, II

The spaceship carrying van Rijn, Adzel and Thea Beldaniel makes rendezvous with a Shenn fleet. Thea joins the Shenna and interprets when they open radio communication with van Rijn. Then the Shenna are joined by Gahood, fresh from his defeat by Falkayn. See here. Van Rijn's influence on Beldaniel has been such that she secretly radios him to say that Gahood has lost Latimer at the rogue planet. She advises van Rijn to flee. But this would probably mean being overhauled and destroyed by the fleet. Van Rijn deduces:

if Latimer, a slave, had merely died, this would not have upset Gahood;
therefore, Gahood probably lost the living Latimer to Falkayn and Chee Lan;
they would then have got the coordinates of Dathyna from Latimer's brain;
they would have proceeded directly to Dathyna for intelligence-gathering purposes;
if van Rijn and Adzel are taken as prisoners/hostages/negotiators to Dathyna, then they will be able to gather more intelligence and might also be able to contact Falkayn and Chee Lan.

Van Rijn shares with two of James Blish's characters the ability to make far-reaching deductions, then to base practical policies on such deductions:

Kit shares with Amalfi, the hero of Cities in Flight, the ability to manipulate populations for remote ends based on abstruse reasoning.
-copied from here.

Van Rijn successfully persuades Beldaniel to persuade her master, Moath, to take him and Adzel to Dathyna. En route, van Rijn is interrogated and thus learns more about the Shenna, especially when he insists on being given more precise questions. For example, Lord Nimran wants to know about occasions when a Terrestrial civilization inherited from an earlier one. Van Rijn cites examples:

Greeks succeeding Minoans;
Western Christendom succeeding the Roman Empire;
Turks succeeding Byzantines;
supplanters like Hindus;
hybrids like Technic or Arabic;
the segue from Classical into Byzantine.

He is confirming that the Shenna inherited their cybernetic technology. He needs to know:

how they did it;
how they can be warlike herbivores;
why they regard coexistence with Technic civilization as impossible.

He is learning which questions to ask.