Agent of Vega is a collection of four stories based on material originally published 1949-51 in Astounding Science Fiction Magazine. It was subsequently published as a book several times. The covers shown are from a 1962 Permabook edition (left), a 1972 Tempo Books edition (middle), and a 1983 ACE edition (right). The four stories in the book include Agent of Vega, The Illusionists, The Truth about Cushgar, and The Second Night of Summer.
The first three stories center around Iliff, a seasoned Zone Agent who is an expert trouble-shooter in the employ of the powerful but over-extended Psychology Service. His assignments are doled out by the Third Coordinator, a highly competent boss whom Iliff loves to despise. The Third Coordinator sends Pagadan, a representative of a new species, to apprentice with Iliff. And when she arrives, Iliff finds himself trailing after his old nemesis, U-1. Iliff is extremely well-balanced mentally about everything except U-1, who once defeated him and left him for dead. The Third Coordinator has evaluated, and uses, Iliff's sensitivity about this humiliation. Iliff knows how he is being manipulated and hates it, but he hates U-1 enough to endure it.
Zone Agent Iliff's disgruntled cynicism, and the razor-sharp dialogue between him and his boss, the Third Coordinator, make this a very fun read. The situations which the Zone Agents investigate are also quite intriguing. These are "good" psi cops chasing "very bad" runaway psi's who are menacing those around them and could only be stopped by other psi's. The bad gize have to get very bad indeed before the Psychology Service gets motivated to send someone after them. As usual, Schmitz' plots become very creative yet stay within rational boundaries.
I found the first three stories very rewarding, and the last one a little less so. The last one deals with a different Zone Agent who is not quite as captivating as Iliff.