"I am nothing. Nothing but a pale shape, silhouetted that evening against the cafe terrace, waiting for the rain to stop; the shower had started when Hutte left me." p.1
"Strange people. The kind that leave the merest blur behind, soon vanished. Hutte and I often used to talk about these traceless beings. They spring up pit of nothing one fine day and return there, having sparkled a little. ... Most of them even when alive, had no more substance than stream which will never condense. Hutte, for instance, used to quote the case of a fellow he called "the beach man." This man had spent forty years of his life on beaches or by the sides of swimming people, chatting pleasantly with summer visitors and rich idlers. He is to be seen, in his bathing costume, in the corners and backgrounds of thousands of holiday snaps, among groups of happy people, but no one knew his name and why he was there. And no one noticed when one day he vanished from the photographs. I did not dare tell Hutte, but I felt that "the beach man" was myself. Though it would not have surprised him if I had confessed it. Hutte was always saying that, in the end, we were all "beach men" and that "the sand"--I am quoting his own words--"keeps the traces of our footsteps only a few moments." p. 47
"I believe that the entrance-halls of buildings still retain the echo of footsteps of those who used to cross them and who have since vanished. Something continues to vibrate after they have gone, fading waves,, but which can still be picked up if one listens carefully. Perhaps, after all, I never was this Pedro McEvoy, I was nothing, but waves passed through me, sometimes faint, sometimes stronger, and all these scattered echoes afloat in the air crystallized and there I was." p.84
"I turned around and stood a moment on the quay. I watched the cars passing and the lights, on the other side of the Seine, near the Camp-de-Mars. Maybe some part of my life still survived there, in a small apartment overlooking the gardens, some person who had known me and who still remembered me." -p.161
Although I believe "Missing Person" concerns the memory (and forgetting) of the Occupation era, I still think the phrase "an existential detective story" is an apt description of the work. I cannot resist the temptation to summarize the first and the last excerpts above in the following sentence: I am nothing--nothing but how I am Regarded and remembered by the Other. (It is also interesting that the main narrator starts searching for his own identity when his long-time friend and employer retires and leaves him alone in Paris.)
Interestingly though, the novel, written mostly in the first-person perspective, records the experience of "I," not how "I" is seen by the Other. It probably is no accident that three brief chapters are there to offer three other characters' perspectives on the main narrator. But these chapters are brief and their accounts superficial. It is how "I" see other characters that constitutes the main stream of the novel. And in the end, it is in the descriptions of the subjective experience of "I"--in those "waves passed though me"--that the reader finds him.