Dragons' Den is back in business, with a brand new fire-breather taking one of the five famous chairs.The youngest-ever Dragon, Steven Bartlett, certainly comes out fighting in his first episode, alongside familiar faces Peter Jones, Deborah Meaden, Touker Suleyman and Sara Davies.Tonight, a couple of 21st-century cheesemongers reveal they have sunk an astronomical sum of money into their new app, emotions run high as a hair technician tangles with the fearsome five, a Scottish entrepreneur presents a pint-sized gadget that he hopes will be big business, and a robotic invention sends the Dragons into a virtual world.