Pickwick is a friend of the Ten Boom family. He is also a leader in the underground, and it is he who first connects the Ten Booms with the resources they need to help Haarlem's Jews.
Pickwick is a large, balding gentleman with a "vast stomach". The family had known and loved him for some time, but when their "operation" in helping Jews escape the Nazis grows to the point to where they need more assistance, young Kik takes his Aunt Corrie to see Pickwick at a meeting of the resistance group in which he is active. This "underground" serves as a "liaison with England and the Free Dutch forces fighting elsewhere on the continent...(and) maintain(s) the underground route through which downed Allied plane crews (reach) the North Sea coast". The group, through Pickwick, are "instantly sympathetic with (Corrie's) efforts to help Haarlem's Jews", and arrange for a secret room to be constructed in her home, in which the Jews can hide in case the Nazis come. They also manage to rig up a telephone warning system in the house, and Pickwick communicates information to Corrie about both Annaliese and Peter when they are each arrested for a time (Chapter 6).
Pickwick is arrested in the same sweep in which the Ten Booms are taken from the Beje, and Corrie remembers him riding in the truck with them when the family is transported to Amsterdam. Pickwick at that time had been brutally beaten, and did not seem to be fully aware of what was going on, and Corrie lost sight of him when they arrived at the prison in Scheveningen (Chapters 9-10). Corrie hears that Pickwick has been released along with Peter and Willem while she is being held in solitary at Scheveningen, but she does not see him again until she herself is set free after her ordeal at Ravensbruck. It is Pickwick, then, who takes Corrie back to Haarlem and the Beje (Chapter 15).