So now we know what all the screeching was about. It was next door's mare making overtures to our stallion (only he's not ours really- he just lives here). Last night he responded and got out of our field and into hers and the mare's owner came knocking on our door after we'd gone to bed (we go to bed very early) to enlist our help. We in our turn enlisted Matthew and Julia because we're just the landowners and know nothing worth knowing about horses. After a lot of clambering through hedges and over fences and standing around talking the situation was partially resolved. Patch was left in the field he'd invaded and his new girlfriend was removed to another one and Chris- who owns Patch- will be taking it from there. It remains a mystery how exactly Patch got from one field to the other. I walked the fence line on my side and the mare's owner walked it on her side and neither of us could spot the breach.