The High Head of Arth is a tyrant only if you insist on taking that term literally. Yes, his word is law on Arth, Yes, he can and will banish someone forever on a whim, and yes, he imposes his own whims and preferences on others without a second thought, but he does all this in the belief that he is working for the Higher Good, and in support of Tradition, and of course because if he didn't run things rather strictly, those damned female mages from Leathe would eat him alive as soon as look at him. The High Head doesn't really trust females.
Therefore, when an abandoned supply capsule suddenly appears in orbit near Arth, with clear indications that there are people on board, it's purely a matter of tradition and proper procedure that causes him to direct his staff to pull the vessel in and see to the people inside it. The fact that these turn out to be females is an extremely unsettling discovery.
As the novel proceeds, we learn more about Brother Lawrence. He comes originally from Leathe, which is governed by female magic users. He was apparently the offspring of a normal Pentarchy female and a gualdian captive, which has given the High Head greater psychic abilities than the run-of-the-mill magician. He has a poor digestion, and can really only stomach the most tasteless grain on the planet, called "passet," in its most tasteless preparations. He tells lies when necessary, and even when not strictly necessary. He has only one friend on Arth -- the level-headed, patient, rational head of Healing Horn, Brother Edward.
And he is the analogue of someone on Earth whose widow has decided that it's just about time to visit this world of Arth and find out who's responsible for all the dirty work that's messing things up on her own planet.
And when that finally happens, look out!