With the bulk of the UK population staying in their homes for fear of getting infected by the coronavirus, this documentary looks at just how safe it is behind closed doors. Two families have their houses forensically swept for fingerprints to find evidence of what they may be unwittingly spreading around. There is also a look at how Covid-19 uses people's behaviour to get inside in the first place and a round-up of the best products to stop the virus in its tracks - and which ones will do no good.