After cracking their first case together, Slim and Dean are certain of one thing-being a Woodstock Irregular means trouble is never far behind. This time, rumors swirl around a long-abandoned house said to hide a fortune in gold bullion. But the boys soon discover the real danger isn't just the treasure. Sneaky thieves are closing in, secrets run deeper than anyone suspects, and a hidden tunnel beneath the house may be the key to everything-or their biggest mistake yet. With Arlen Bailey and Danny Black back at their side, Slim and Dean plunge into secret clues, nighttime schemes, and close calls that test their courage and loyalty. Help comes from Treasury Department Agent Mason and the ever-watchful sheriff's deputy, Mr. Kingsman, but even grown-ups can't always keep the Irregulars out of trouble. Set once again in 1960s Woodstock, Wisconsin, Mystery of the Abandoned House blends suspense, humor, and classic kid-led sleuthing as four friends race through dark passageways and dangerous twists to uncover the truth before it vanishes forever.