A jealous wife tried to poison her Navy officer husband on three occasions in an attempt to make him confess to having an affair.
Businesswoman Linda Lees, 45, twice put poison in her husband Paul's takeaway after their 23-year marriage collapsed.
And during a meal at a restaurant she asked a waiter if she could hide her wedding ring in his food as a romantic surprise - but laced his plate with poison instead.
Detectives say Mrs Lees suspected the Royal Navy avionics lecturer, 43, of being unfaithful, and administered an unnamed toxin to try and coax him into admitting his infidelity.
She is said to have made the repeated attempts despite having a long-term affair with a neighbour herself.
Police are still waiting to find out what drugs she used in the last attack but believe she used those prescribed for her own depression.
They are investigating if she may also have used the date rape drug GHB.
Lees, the manager of a car rental company, admitted administering a noxious substance with intent to injure her husband, who is based in Portsmouth, on three occasions.
The first was at her home in Cornwall when he visited for a weekend in March and the second was at a restaurant in Exeter where they met to try to save their marriage the following month.
Finally, she poisoned him again ten days ago when the couple, who have a 21-year-old daughter, decided to spend a last weekend together walking along the Cornish coast.
She put more drugs in his Chinese take-away and left him semi-conscious at home while she tried to commit suicide in the garage of their marital home in Helston, Cornwall.
She is believed to have survived because her car had a catalytic converter, reducing the amount of Carbon Monoxide she inhaled.
Both were taken to hospital and survived without permanent injury.
After Lees pleaded guilty to three charges of administering a noxious thing with intent to injure, aggrieve or annoy, Detective Constable Martin Skinner said: 'This really was a crime of passion.
'It is fair to say there had been a strained relationship throughout the 23 years they had been married.
'Paul Lees is in the forces and his long absences led to the relationship deteriorating.
'They owned a house together in Cornwall but he worked elsewhere and six months ago he decided the relationship was definitely going to end.
'At the time she accepted it and agreed with him and hid the fact it was not what she wanted.
'That is why she took the drastic action of attempting to stupefy him - it appears she may have been trying to find out if he had any other relationship going on.
DC Skinner added: 'Mrs Lees had been having an affair with a man four doors down from her who was also a friend of Paul's.
'The relationship [with her husband] had been strained and was coming to an end, but neither of the couple wanted to admit it.
'She had suspicions of an affair and took drastic action to find out about his relationship.'
During the restaurant poisoning, Mrs Lees went to the toilet and stopped a waiter to ask if she could put a ring into her husband's food as a surprise.
But she then slipped poison into it and calmly watched as he ate his meal.
On the third poisoning in July Mr Lees, 43, travelled to the marital home where the pair ordered a takeaway and Mrs Lees poisoned it once again.
After the meal she took him for a drive and by the time they arrived back he was severely drowsy but managed to escape the car and let himself into the house.
She then went to her lover to confess to the poisoning before later returning to the garage where she tried to take her own life.
DC Skinner said: 'When police arrived they found her in the car with a hosepipe attached to the exhaust. It was her lover who called the police.'
Mrs Lees made a full confession and said she 'knew it was wrong but could not stop it', according to DC Skinner.
Terry Eastwood, defending, said there would be a delay in sentencing while a psychological report is completed.
The couple's daughter Hannah, 21, attended the hearing where Lees was granted bail on the condition that she live with her mother at an address in Helston and obey a night time curfew.
She was also barred from attempting to contact her husband. She will be sentenced in October.