When Brown Bear wakes from his long winter sleep, he hears a mysterious sound. Unable to identify it, he sets out to discover where the strange noise is coming from. Through field and forest, he spends all spring, summer and fall searching for the source of the ?thump-bump? sound that follows him wherever he goes. Finally, Brown Bear returns to his cave, where he prepares to settle in for his winter nap. Only then does he discover that the noise is the beating of his own heart.