The final part of this all-access series follows the rail mobile detection team as they discover a high-tech home, complete with electricity, running water and TV - illegally erected under an arch beside one of the country's busiest areas of track. But can they find the culprit?
At Euston, there's no rest for British Transport Police officers as they're called on to back up platform staff when tempers flare - and to deal with an unusual Royal request.
And a strike hits Birmingham New Street Station and the rail network - on one of the busiest days of the year. With industrial action on West Midlands Trains, many passengers are left high and dry and it's down to Network Rail to deliver the bad news.