
According to reports Marvel Comics' 'The Inhumans' will appear in the new season of "Agents Of S.H.I.E.L.D.":

"The Inhumans", created by writer Lee and illustrator/co-plotter Jack Kirby, debuted in Marvel's "Fantastic Four" #45 (December 1965).

Millions of years ago, at the beginning of the alien 'Kree'-'Skrull' war, the Kree set up an observation station on the planet Uranus, to observe sentient life on Earth that had genetic potential.
The Kree then began to experiment on homo sapiens by splicing 'Eternals' DNA into 'Cro-Magnons', to investigate ways of circumventing their own evolutionary stagnation, while creating a powerful strain of soldiers for protection against the Skrulls.
The Kree then began to experiment on homo sapiens by splicing 'Eternals' DNA into 'Cro-Magnons', to investigate ways of circumventing their own evolutionary stagnation, while creating a powerful strain of soldiers for protection against the Skrulls.

Their test subjects, that became to be known as the 'Inhumans', formed their own society, thriving in seclusion from the rest of humanity, developing their own advanced technology, including the mutagenic 'Terrigen Mist' which gave them superpowers.