Gench and Pewsey were formerly ruthless air-pirates. Even though it is not said how he and Pewsey were reformed and came to work aboard London, it is possible that he and Pewsey's airship was shot down by a London airship and both were taken aboard London.
Gench and Pewsey attacked the Jenny Haniver, which was flying over London. They shot rockets at the Jenny, hurting its pilot, Tom Natsworthy. However, Tom fought back by shooting rockets at the Elevator's windows, killing Gench and Pewsey. But Tom regrets killing him and Pewsey soon after London is destroyed by MEDUSA.