"What is fire? Is it a solid, liquid or a gas? Why is it hot and why can you see it in the dark?" asks Hannah Norton, aged 10.
Dr Fry visits the Burn Hall at The Buildings Research Establishment in Watford where they test the effects of fire on building materials.
Whilst Dr Rutherford gets to grips with Michael Faraday's pioneering Christmas Lectures at the Royal Institution of Great Britain on 'The Chemical History of a Candle'. Plus, he chats to forensic chemist Niamh Nic Daeid from Dundee University about our lasting fascination with fire.
You can send your Curious Cases for the team to investigate to: curiouscases@bbc.co.uk
Presenters: Hannah Fry, Adam Rutherford Producer: Michelle Martin.