Having hired Eric Catchpole as an apprentice, Lovejoy sets out to unravel the meaning of a Japanese firefly cage.As Lovejoy and Eric are in hot pursuit (on Eric's motorbike) of a lovely lady with something they want, they hit a pool of water in the road and give a drenching to Jane (Lady Felsham), who is busy unveiling a plaque. When, later, Lovejoy rings the doorbell at Felsham Hall, complex chemistry begins, and Jane is soon showing Lovejoy around her attic...

A robbery at the local museum seems to be connected with the death of a local forger, and Lovejoy goes on the trail of a hoard of Roman coins in the Isle of Man. Two Americans are also after the coins.

Lovejoy travels to Venice to investigate the murder of a friend. The dead friend had bought a painting Lovejoy believed was a fake. In Venice, he is drawn into an ambitious art swindle, and identical twins Caterina and Lavinia are behind the scam.