For MI5 Intelligence Officer Liz Carlyle the nagging complications of her private life are quickly forgotten at Monday's Counter-Terrorist meeting. An invisible may have entered mainland Britain. An 'invisible'
- a terrorist who is an ethnic native of the target country who can cross its borders unchecked & move about unnoticed
- is the ultimate nightmare. For Liz this signals the start of an operation that will test her to the limit. Who or what is the target? Where & who is the invisible? With each passing hour the danger increases. But as she desperately sifts the incoming intelligence & analyses the reports from her agents she finally realises that it is her ability to get inside her enemy's head that is the only hope of averting disaster.