It was a quarter to midnight and the River Thames was quiet after the day's activities. Soft orange light together with the sound of loud bawdy humour poured out of the taverns that were dotted alongside the riverbank.

Out on the water, three dark-dressed figures sat in a rowing boat as it slinked silently between the coal barges, making its way to the Tower of London.

James Carter had slipped the small craft off its moorings at St Katherines Dock earlier in the evening. He assured Harriet that it would be back before its owner could report it missing.

The dark outline of the iconic fortress loomed into view and along the side of the embankment, James eventually saw the black mouth that was the entrance to 'Traitors Gate.'

All three of them pulled their black hoods over their heads as James rowed through the archway. He berthed the small craft and while he secured the boat, Agatha helped Harriet carry the tripod and the box camera time machine up the slimy stone steps.

Time was pressing, so Harriet hastily erected the tripod placing the box camera on top then she pointed it away from the river towards the huge clearing that was Tower Green.

Harriet fussed around the camera checking that nothing had become dislodged during their river voyage. She then gave a final glance at her watch, four minutes to midnight. Removing the lens cap, there was nothing to do now but wait.

"I hope you get to go back in time to be with your mother?" said Agatha.

"I have been thinking about that, my...