The mysterious last adventure of Mrs Unwin

What made Tory activist set sail on her fatal trip? David Randall on the missing newlywed's complex life

Last night, a week after she left a Cornish port to sail to her north Devon home, there was still no sign of Mary Unwin, or her body. Despite the scrambling of three lifeboats, two helicopters, a plane, cliff rescue parties, and no fewer than 150 coastguard staff, all that has been found so far are a few broken pieces of the boat she had purchased just three days before.

Heaven knows what was going through her mind to think she could sail single-handedly in the dark, through stormy October weather, 140 nautical miles round Land's End. Everyone who knows this rocky and treacherous coast described her plan as reckless to the point of insanity. So what caused this newly remarried 65-year-old Conservative activist, Facebook friend of Jeremy Hunt and Liam Fox, organiser of Tory women's lunches, and past employee of a village post office to set off on a doomed voyage that would bring out half the air-sea rescue forces in the South-west?

The story of Mary Unwin that can be pieced together this weekend – and it is by no means complete – is not a straightforward one. She has been widely referred to in the media as a millionairess, a description wide of the mark, according to her husband's family. (Her own family politely declined to talk to us.) But of the fact that she was a forceful personality – popular and engaging say friends and acquaintances, but headstrong, even, and certainly a character – there is no doubt.

She was born Ona Mary Davies in Gower, south Wales in 1947, and, according to her Facebook page, attended Swansea Law School, had and then cared for her children, gained a qualification in voluntary work, and was employed by the Post Office. From the tone of her entries, it seems clear she had more vitality than some people half her age, and this seems to have extended to marriages. The Daily Mail reported yesterday that there have been five of these, with the first coming in 1964 when she was 17. Official records show that an Ona M Davies was married in 1964, 1980, 1990, 2002 and 2012. We have been unable to confirm that all five of these are this Ona M Davies, although her brother-in-law believes this to be the case.

The last two weddings were to Carol John Unwin, four years her junior, and the son of a wealthy couple who owned Longdon Hall, a nine-bedroom historic house outside Tewkesbury, Gloucestershire. Through his mother, the descendant of a baronet, he, and therefore Mary, have a small walk-on part in Burke's Peerage. Carol had a bad motor-racing accident at Brands Hatch when he was 19, and the serious effects of his injuries remain with him, his family say. His brother, the inventor and entrepreneur Guy Darell Unwin, said that widespread reports that Carol was a multi-millionaire property dealer are not true. The only listed directorships we have found are for dissolved companies.

Carol met Mary in 2001 when they both lived in the village of Upton-on-Severn, Worcestershire, and the couple married several months later. They lived in Longdon Hall, from where she threw herself into energetic action with the local Conservative Party, organising women's activities and lunches, and standing as a candidate in local elections. Her Facebook friendships reflect this interest: of the 103 friends listed, many are prominent Conservatives, including Liam Fox, Jeremy Hunt, Tim Montgomerie, Kit Malthouse, and a variety of MPs and MEPs. Only one of those we contacted had ever met her, and that only fleetingly some years ago.

She divorced in 2009, and later that year appeared in a television documentary about online pawnbrokers. She had pawned some jewellery so she could put down a payment on a £98,000 Aston Martin, pending – accounts vary – either her divorce settlement or the maturing of an investment. "I just like nice things," she told the programme, "but I can't always afford them."

Mary and Carol remained in contact, reconciled, moved to a £495,000 bungalow in Northam, near Bideford in Devon, and remarried on 5 October this year in the church at the popular tourist destination of Clovelly. Three of her adult children attended, as did some score or so friends, but the Unwin family were not there. Less than a week later, on Thursday 11 October, Carol and Mary set off in his Porsche to drive down to Falmouth in Cornwall to view his intended wedding present to her: a yacht.

The boat they viewed at Falmouth Yacht Brokers was a 31ft sailing yacht named Seagair, priced at £31,995. They inspected it and discussed a survey, but the surveyor could not crane the boat out of the water until the following Wednesday, something that did not fit into Mary's plans. The boat was paid for by banker's draft (which, as of early Friday afternoon had not cleared – such transactions can take 10 days to complete). Mary told Jayne Hobkirk, a director of Falmouth Yacht Brokers, that she had a "navy ticket", but Ms Hobkirk urged her to take a refresher course. This was duly booked, and during the few hours she spent with an instructor, he told her not to take the boat out on her own. She inquired about a skipper, but one could not immediately be found. And so, the following day, Carol having driven back to Bideford, Mary set off on her own. Her intention was to sail round the Cornish peninsular to north Devon – a distance of around 140 nautical miles,

She reached Mousehole on Saturday, and spoke to two fishermen whom she asked to help her tie up the boat. She told them her plan to set off for Devon on the evening tide, and they expressed amazement at such a single-handed trip by a pensioner, in the dark, with a swell approaching five feet, winds varying around and above Force 5, without a beacon, and in a boat possibly lacking a functioning radio or charts. "No different," she told them, "to driving a car at night" – a remark that belies her husband's claim that she was an experienced sailor.

One friend, and the instructor in Cornwall, said she showed them a coastal skipper's certificate of some vintage, but her brother-in-law said yesterday he had never known her go sailing in the 10 years he had known her. And yet, at 6.30pm last Friday, with darkness almost fallen, she set sail. As she left, she bumped into the quayside.

That was the last anyone saw of her. When she failed to show up in Devon on Sunday evening, the alarm was raised and the extensive search launched. On Monday, a large part of the cockpit and other smaller fragments of the boat were found near Sennen Cove, just north of Land's End. No one outside some outlandish postings on online forums doubts that she can be anything other than presumed dead. Devon and Cornwall Police say there are no suspicious circumstances.

No one who knew her well thinks that she was at all suicidal. Reckless, perhaps; disinclined to take advice, certainly; but not likely to kill herself. Was it also an attempt by a woman of advancing years to prove herself? An adventure by someone whose marital history and appearance on television suggests she was a stranger to caution? Barring some extraordinary development, it's unlikely we'll ever know.

Additonal reporting by Daisy Stenham