Solitary plasmacytomas (SPs) are tumors characterized by local monoclonal plasma cell proliferation, presenting without systemic manifestations. It mainly affects the axial skeleton, with calcaneal involvement being extremely rare. We report a case of a 48-year-old patient with a history of gunshot injury to his foot who presented with worsening heel pain and a calcaneal cyst. Biopsy revealed plasmacytoma, and subsequent 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) scan further supported the diagnosis of solitary plasmacytoma of the bone (SPB). Management included lesion excision, bone cement placement, and radiotherapy. However, due to recurrent osteomyelitis following cement placement, the patient eventually required total calcanectomy. SPB usually affects older adults, and developing the disease at a young age and in the calcaneus is exceedingly uncommon. Trauma is implicated as a possible inciting trigger in the pathogenesis of SPB without a clear association. This case highlights the importance of developing our current understanding of the clinical presentation and manifestations of SPB, beyond the conventional assumption that it only affects the axial skeleton of older individuals.