Bill Brand, aka the Black Rider, is an agent for British military intelligence.
The year is 1914 and the Great War had just recently begun. In one of the first "desperate battles" that the British Expeditionary Force has with German troops, a mysterious motorcycle rider dressed in black upsets the horse being ridden by a British Captain. That officer, quite irked, orders his Company Dispatch Rider, Corporal Bill Brand, to pursue the man to arrest him. Even though he was on a bicycle, Brand gamely gave chase but several miles down the road, two unfortunate events take place. First, the rider gets away. Second, German forces had advanced quickly and Brand was in danger of being captured, on foot with a busted bike. At that moment, the motorcyclist reappears and orders a startled Brand to jump into the sidecar. The two barely make their escape but not before the cyclist, a Major Rudd, was wounded.
"Expert motorcyclists are rare birds, corporal, the head of the Military Intelligence unit they finally made it to. "You were indirectly responsible for our Major Rudd being seriously wounded, so I suggest that you take over where he left off".
That is how a novice motorcyclist but apparently gifted bicyclist took to wearing the all black leathers and becoming an operative for Military Intelligence behind enemy lies.
It is at this time that Brand learns that the previous rider had been "a clever scientist [who] fitted various gadgets to the machine", nifty little odds-and-ends, such as an oil slick dispenser, which will come in quite handy as Brand, the new Black Rider, is sent on a variety of important and dangerous missions.
Some of the other gadgets include a level to activate a "special safety harness" in the sidecar to hold prisoners as well as an ejector seat button there to throw out undesired passengers.
Another switch puts spikes on his wheels allowing for mountain climbing. He also has the ability to put treads on the wheels to make traveling on sand possible.
In a special compartment at the front of the sidecar is a pop-up machine gun! That compartment also has a side window for a flame thrower.
Naturally he would have some method to silence his engines for when stealth riding is needed.
We learn very little about Bill Brand, other than he is very resourceful and totally intrepid, but we learn a great deal about his vehicle, the real hero of this series.