A to Z Challenge - N is for New Evidence

The A to Z challenge is to write a daily blog post centred around a different letter of the alphabet each day. I will attempt to write a complete story which will continue each day and hopefully draw to a conclusion when we get to Z.
For previous posts click a letter - A , B , C , D, E , F , G, H, I,  J, K, L, M
 

DI MacDonald arrived back at the office and settled down at his desk. He loved his desk, it was so ordered, with everything where it should be. The blotter in the middle with...