The Tale of the Unknown Island by José Saramago

That night, Senhor José returned to the Central Registry. He took with him the flashlight and a hundred-yard roll of strong string. He had put a new battery in his flashlight that would suffice for several hours of continual use, but, more than chastened by the difficulties he had been obliged to confront during the dangerous break-in and theft at the school, Senhor José had learned that in life you can never be too careful, especially when you abandon the straight paths of honest behaviour and wander off down the tortuous shortcuts of crime.

What if the little bulb were to blow, what if the lens that protects and intensifies the light were to come loose from the casing, what if the flashlight, with the battery lens and bulb intact, were to fall down a hole so that he couldn't reach it with his arm or even with a hook, then, not daring to use the real Ariadne's thread, despite the fact that the drawer in the Registrar's Office where it was kept, along with a powerful flashlight, was never locked, Senhor José will instead use an ordinary, rustic ball of string bought at the hardware store, and that string will lead back to the world of the living the person who, at this very moment, is preparing to enter the kingdom of the dead.