God of the Hive by Laurie R King (2010) Bantam

Mary Russell and her husband, Sherlock Holmes try to rescue his son, Damien.  Reverend Brothers has survived the incident on Orkney Island, but when he checks-in with his benefactor, he is killed.  Holmes and Russell do not know this.  Russell, with Damien’s daughter connect with a pilot (who took her north in the previous volume) and attempt to fly back to London but are shot at on the way and crash in a forest.  A man who seems like the Green Man, rescues them and gives them shelter.  Holmes older brother Mycroft has been abducted and has his life threatened.  A group of men invade the green man’s home but are stranded when the green man leads Russell and party to their car.  The green man turns out to be a war hero with a tainted past and son of a Lord.  Russell discovers a key in Mycroft’s home and tracks it to a woman who says the key hasn’t been used in ages and in fact the lock was changed years ago.  She also discovers that Mycroft’s secretary has been receiving large sums of money from an unknown source, especially just after Mycroft’s disappearance and then mysteriously disappeared himself.  Holmes has his some secreted away in Holland but returns to London to solve the mystery.  The story culminates with all parties coming together.