WE are all susceptible to deception, both by ourselves and by others. Yet we all like to think we can detect the phoneys and sociopaths from a mile off. Closer to the truth is this: we tend to believe what we need and want to believe, especially in matters of the heart.

The heinous murder in April 2016 of author, Helen Bailey, by her fiancé, Ian Stewart, is chilling. Stewart, who's been sentenced to 34 years imprisonment for the drugging and murder of Helen Bailey, was, by all accounts, a dyed in the wool sociopath. It appears that Helen Bailey was besotted by Stewart and trusted him with her life. Days before her murder, she was Google-searching for wedding reception venues, and for answers to the question: "Why do I keep falling asleep in the middle of the day?" (Stewart had, for months, been sedating her with sleeping tablets mixed into her morning scrambled eggs before finally smothering her, then burying her body in a cesspit below their garage.) His motive appears to have been financial gain as Bailey was extremely wealthy and Stewart was the main beneficiary of her will. Reading and watching the news reports, we can all cry out, pantomime style, from the stalls: “He's behind you, look behind you!” But in cases like this, where a sociopath "love-bombs" their victim in order to trap them before they move in for the kill, it can be extremely difficult to see the wood for the trees. This is not because of stupidity or naivety, but because as humans, we have a strong need to love and be loved. And who among us has not been stung, even if only in passing, by the narcissist or sociopath when it comes to romantic liaisons? With the innocence of children, many of us, though adult, trust that if we love openly and wholeheartedly, we will be loved similarly in return. Statistics vary, but it is generally believed that between 1-4 per cent of the population have anti-social personality disorders such as sociopathy. Fortunately, most of us don't end up married to a sociopath. But if, like Helen Bailey, you are unlucky enough to be caught up in their net of manipulation, it is unlikely that you will come out of it unscathed.

Sociopaths (and psychopaths) are injurious to emotional and mental health. They don't fall in love. Instead, they scan for suitable targets and devise a strategy. A suitable target is often someone who is vulnerable, or in crisis (when Helen Bailey first met Stewart, she was grieving the recent death of her husband who drowned in front of her in 2011). Other essential requirements on the sociopath’s victim hit list are qualities such as empathy (they need sympathetic listeners for they always have a tragic back story crafted around betrayal by others or just plain old bad luck). They'll also zoom in on people who have a tendency to see the best in others. Throw in a measure of low self-esteem or loneliness, and the sociopath has an ideal candidate.

When it comes to romance, sociopaths lock onto their victims like heat-seeking missiles. Their eye contact is powerful, seductive and unflinching (rarely do they look away when they have you in their gaze). In the bedroom, they don't make love, but perform (often very well because exciting sex is another way of having mastery over their victims). They are predators who see people as objects to be moved around the stage in their theatre of manipulation. They are expert mimics and can fake "real" feelings at the drop of a hat (they just can't "feel" feelings). They will convince you that you are the love of their life, truly special. They always accelerate relationships, leaving little time or space for partners to have emotional autonomy. Their preferred modus operandi is the whirlwind romance.

The problem is that, like deadly nerve gases such as Sarin or VX (used recently to kill the North Korean Kim Jong-nam at Kula Lumpur airport) which are odourless and invisible, sociopaths can be hard to detect. They dedicate themselves to blending in, to being Mr or Mrs Nice. In order to spot them, you need a degree of objectivity, and what the late, great scientist and philosopher, Carl Sagan, described as a "Baloney Detection Kit". In his essay on Baloney Detection, he encourages all of us to employ healthy scepticism and analysis of the facts, the evidence of our own eyes. If we are prepared to put our own desires and needs under the microscope of self-analysis and critical thinking, we are much better placed to understand how they work – their strengths and weaknesses. This is the best line of defence against the hostile takeovers so beloved by sociopaths.