It was Nick Proffitt who coined the phrase. On the evening in 1972 when I first heard it, I was at his villa in Saigon, sitting on the big veranda that overlooked a bigger garden that in the moonlight looked mysterious, possibly mined, whence emanated the plaintive calls of geckos, nocturnal lizards, saying "uh-oh" over and over again. I was a fledgling war correspondent, aged 24, and Nick, a colleague, was my first friend in Vietnam. On many nights I'd stay at his house past the eleven o'clock curfew, when the city was silent and disquietude rose from the empty streets, and we'd sit enclosed in the humidity talking endlessly about the war. We thought we knew a secret nobody in the States knew, and burned with our frustration in communicating it. As soon as Nick mentioned the mark, I knew I had it, I knew we both did. Having the mark meant being addicted to Vietnam, being used to intrigue and pumping adrenaline and layer after layer of lie, truth, lie, truth, until the two were indistinguishable; the mark was the perverse and frightened expression of our love. People with the mark shared a yearning they suspected Vietnam of being able to satisfy, and while they hated the war (for wars are meant to be hated), they loved it even more, and hated themselves for loving it.

The mark was alchemical. It transformed sordid objects into things of wonder, even beauty; it made fear tolerable. Under its spell I'd leave Nick's villa at midnight or so, nodding goodbye to him as he closed the hulking metal gate behind me, and then I'd be alone on the street, exposed. It was at that spot that Nick's terrified successor, Lloyd Norman, once was held up by a man who put his hand inside his jacket pocket and made it look like a pistol, and by doing so managed to relieve Lloyd of his wallet and watch; in a country distinguished by the scope of its violence, the thief struck me as quaintly pacific, nearly gentlemanly. I'd stride down the street, stunned that the moon could shine so brightly over such benighted ground: it gave everything a silver outline, like Jesus in a medieval painting. I'd see the silhouette of the Vietnamese soldier who manned the outpost on the corner, and I'd try to show him by my pace and stature that I was an American, before he lifted his rifle and looked through the crosshairs. Usually he didn't even acknowledge me: I learned to feel relieved when my presence failed to evoke the slightest movement in him. I'd walk past the Catholic cathedral where the daughter of South Vietnam's president would get married within days of the climax of nearly five years of peace negotiations, and fancy cars would line up outside as if their high-ranking occupants were filled with the joy of matrimony instead of the trepidation that everyone knew gripped the city. I'd pass by the park where lovers gathered on their motorcycles in the early evening and then raced home to beat the curfew, and I'd feel the longing and desperation of their romances— it was like a haze they'd left to settle over the park after they'd gone home. Down the street was the Presidential palace itself, the very seat of foreboding, wreathed in shadows, nearly invisible, ringed by layers of barricades; I'd imagine President Thieu, as stolid and graceless as the edifice he inhabited, sitting at its core, endlessly calculating the logarithms of killing, and I'd shudder as the sinister emanations passed through me. As I walked, I'd hear the outgoing artillery in the distance, either deadly or futile, no one ever knew which. At least I'd reach my courtyard and unlock the metal door and walk up the circular staircase to my villa, through the living room with its checkerboard floor and its bar adorned with rice straw, and I'd take one last look through the lattice windows at the park and the palace and the cathedral. It took only five minutes from Nick's house to mine, but by the time I reached home I could feel my heart pumping, and I'd know that I never wanted to live in any place where evening walks offered less drama. In Vietnam I'd found my universe of darkness and light, the font of all my feeling. My mark was deep.