make a fire, Dr Oliver,’ he said. ‘You need heat, a fuel source such as paper or gasoline, and you need oxygen. Without any one of those, no fire.
Do you understand?’
Evi nodded.
‘In most circumstances, we can take the oxygen bit for granted. So, what we’re looking for is a combination of heat and fuel. After that, fire travels sideways and upwards from its point of origin. If a fire occurs at the foot of a wall, you’ll see the burn patterns spreading up and away from it in a V shape. Are you with me?’
Evi nodded again.
‘Some things in a house, like synthetic materials or stairways, can distort this, but as a rule of thumb you track the fire damage back to the point at which it was greatest and then look for the heat-and-fuel combination. At the Wite Cottage fire, the point of origin was pretty clear, even though the upper floor eventually collapsed. It was the kitchen, the area around the cooker.’
‘And do you know how it started?’ asked Evi.
‘Largely guesswork,’ replied Blake, ‘because the damage in the area was so extensive. But we understand cooking oils were kept around the cooker, never a good idea. We suspect a pan was left with a gas flame underneath. It happens a lot with omelette pans. People make an omelette, concentrate on tipping it on to a plate without breaking it and they put the pan down, forgetting they’ve not turned the gas off. The pan gets hotter and hotter until the oil left in it catches light. If a plastic bottle of olive oil was close by, the plastic would melt and the oil run out. You can see how …’
‘Yes, of course,’ said Evi, making a mental note to move the bottles of cooking oil she kept close to her own hob.
‘In this case, though, the real problem was the Calor gas,’ said Earnshaw. ‘The cottage wasn’t connected up to the mains gas supply, so the family used a cooker that was powered by Calor gas. It’s not uncommon in rural areas, but in this case, the family had three spare canisters stored in a small room just to one side of the cooker. Once they caught fire …’
‘I see,’ said Evi, wondering if she really had the nerve to ask her next question. ‘I know this is a difficult question and please excuse me for asking it, but did you ever consider the possibility of arson?’
Earnshaw leaned back in his chair. Blake was frowning at her.
‘We always have to consider arson,’ said Earnshaw after a while.
‘But on this occasion, there was nothing to cause us any undue concern. The fire had an easily identifiable point of origin.’
‘One that could be readily explained,’ chipped in Blake.
‘Had it started in a wastepaper bin in a bedroom,’ said Earnshaw, ‘or if we’d found a trail of petrol around the house, it would have been a different matter.’
‘The house was rented, so there was no possibility of insurance fraud,’ said Blake.
‘And the couple lost their child,’ said Earnshaw, as though Evi should have thought of that herself. The arson-to-disguise-accidental-death theory wasn’t going anywhere. Evi began to think she might be outstaying her welcome.
‘I do understand that,’ she said. ‘I know I’m asking insensitive questions. I’m sorry I can’t explain why.’
‘Hiding evidence of arson really isn’t that simple,’ said Blake. ‘Arsonists often use matches and then just throw them away, thinking the fire will destroy them.’
‘And it doesn’t?’
Blake shook his head. ‘Match heads contain something called diatoms,’ he said. ‘Single-celled organisms containing a very tough compound called silica. Silica survives fires. Sometimes we can even identify the brand of match used.’
‘I see,’ said Evi. ‘I’ve got one last question, if I may, then I’ll leave you in peace. How soon after the fire was extinguished did you realize that the child’s body had been completely destroyed?’
The two men looked at each other. Blake’s frown had deepened.
‘The fire burned for several hours, I understand,’ Evi went on. ‘Even after it was extinguished, you would have had to be sure the structure was safe.’
‘The upper floor collapsed,’ said Blake.
‘Yes, exactly,’ said Evi. ‘So you would have had to search through the wreckage, it must have taken quite some time, before you were sure.’ And all that time, Gillian had been traipsing over the moors, willing herself to keep believing. ‘Before you were sure the fire had obliterated the child’s body.’
‘Dr Oliver, it’s very rare for bodies to be completely destroyed in fire. Very rare