Saul was Hetty's foster brother who she extremely disliked and never got on with as he always was mean to her and prodded her with his stick as he was a crippled boy from birth she in return pushed him off a tree and into a pig sty. When he was to leave for the Foundling Hospital, Hetty realizes she was a bad sister to him and screams at her foster mother and sister intending him to stay. When Hetty is in the hospital, she dresses up as a boy and finds Gideon where Saul was there also. He tells her, Hetty, you told Gideon to remember but you forgot me!!. Later on in the book, it is the Flu/Influenza season and Hetty catches it but survives and is Okay again but Saul and another girl named Sarah Barnes also catch it and sadly, they died. Hetty never really forgive herself for that and was very upset and felt she was a bad sister to him. In Sapphire Battersea, she meets a lady called Madam Berenice who was a fake spiritualistic Saul has returned! Hetty gets scared and realizes the same mistake she did when she was a little girl and run out of the house. 

That's all there is information of Saul.