When history teacher, Bear Hoskins, with an unusual fascination for borders meets sales rep Sophie Bingham on holiday in Portugal, she absent-mindedly leaves behind a precious item of jewellery. Reuniting the owner with her property is merely the first in a series of challenges as they each have to fend off colleagues' amused enquiries at their unconventional developing relationship. The unlikely appearance of a persistent Portuguese antiques dealer suggests that there is more to their apparently chance encounter than meets the eye. The growing mystical significance of the number four impresses itself uncannily on Bear and Sophie as their pursuit of truth intensifies.