Before the beginning was the gate.
And five gatekeepers...Four boys, One girl. The gate is about to open. The gatekeepers must return.
 -Exerpt from Raven's Gate, Book 1.

The Gatekeepers are these five children. All of them possess special powers and were alive thousands of years ago, three under different names. At the time there were malevolent beings called The Old Ones. Their aim was to enslave all of humanity and destroy it slowly, as they feed on misery and pain.

But these five children stopped them, and The Old Ones were sealed behind two gates, one in Yorkshire, the other in the Nazca Desert, Peru. Now in the present year, Matt Freeman , the first of the Five, stopped The Old Ones breaking through Raven's Gate. However, he was mortally wounded in the battle for the second gate, and The Old Ones were released into the world, albiet badly wounded by Matt.

The Five can use their powers on their own, but when they are with each other, their powers are stronger. When Matt , Pedro , Scott Tyler  and Jamie Tyler are fighting in their home in Peru, Matt is described to be able to send the monsters flying away with just a nod, whereas in the first book he isn't able to use his power until almost the end of the book.

The Five constantly face danger in the books, as The Old Ones have followers on Earth who believe that when The Old Ones take over the Earth, they will recieve rewards for what they have done:

Book 1: Matt faced the witches in Yorkshire, particuarly Mrs Deverill and her dribbling slave Noah.

Book 2: Matt and Pedro are pursued by Diego Salamanda, who controlled the entire police force too.

Book 3: Scott is kidnapped by Nightrise Corporation but Jamie escapes, and he is then pursued by Nightrise . Also, Jamie travels back in time to face The Old Ones as Sapling, his past form who is killed.

Book 4: Scarlett is unknowingly trapped by Nightrise and shapechangers who came through the gate with The Old Ones, until she is rescued by the White Lotus Society (also known as the Triads).

Now that The Old Ones have returned to Earth, the Five must unite and destroy them once and for all.