At sixty-two, Elena had never paid much attention to her fingernails beyond keeping them neat. Then, while washing dishes one evening, she noticed a deep horizontal groove crossing several nails. She remembered being sick months earlier and assumed the lines were simply part of aging. Her daughter, however, urged her to look more closely. Elena noticed faint vertical ridges on several fingers too, along with unusual pale bands she had never seen before. She searched for explanations and discovered that some nail changes can follow illness, injury, or periods of physical stress, while others may be connected with nutritional or medical problems. Most were not dangerous, but one warning caught her attention: a new dark streak beneath a nail could sometimes require prompt medical evaluation.

She looked down again, suddenly uneasy. Her right thumbnail had always been slightly uneven, but now she noticed a narrow brown line running beneath it. She could not remember injuring the finger. It seemed darker than it had been the week before. Elena almost dismissed it as a bruise, until she noticed that the mark appeared to be changing. That was the moment her curiosity became something more serious.