The Night of the Morningstar by Peter O'Donnell

Modesty Blaise is about to retire from her criminal empire, the Network, a crime syndicate specialising in art theft and industrial espionage. But there is one final, astounding mission before she can leave and the Network is disbanded. Years later, she faces the consequences of this final mission when she and her faithful lieutenant Willie Garvin find themselves drawn into conflict with the mysterious group known as The Watchmen.

The Watchmen have big plans, not least to destroy the Golden Gate Bridge. Modesty and Willie will need all their cunning to foil a fiendish plot to bring down western civilisation and save their own lives.