Isso soa muito como Stepsons of Terra de Robert Silverberg.
Não consigo encontrar muita informação na Internet ( uma revisão aqui ). Pelo que me lembro, é sobre alguém viajando para a Terra de uma colônia distante para procurar ajuda. Envolve também a clonagem via viagem no tempo.
... um homem cujo planeta seria atacado por alienígenas em um par de anos. Para evitar que seu planeta fosse destruído, ele foi enviado de volta à Terra (a uma grande distância) para obter ajuda.
Already four worlds had fallen to the Klodni since the aliens had begun their campaign of conquest. The timetable said they would reach Corwin within the next decade.
...
Ewing shuddered as his tiny ship spiralled Earthward, bobbing in the thickening layers of atmosphere. Earth will save her colonies from conquest.
A Terra era um planeta cheio de acadêmicos e pessoas pequenas apenas focadas em filosofia e coisas do tipo.
The more Ewing read, the less confident he became that he would find any aid for Corwin here. Earth had become a planet of gentle scholiasts, it seemed; was there anything here that could serve in the struggle against the advancing Klodni?
... a casa foi considerada em um "tempo" diferente. Ele tinha uma chave especial para entrar na casa
Myreck held his key in front of him, stpped into the lot and groped briefly in mid-air, as if searching for an invisible keyhole. And indeed he seemed to find it; the key vanished for three-quarters of its length.
...
Myreck smiled. 'The house is three microseconds out of phase with the rest of the street. It always exists just a fraction of an instant in Absolute Past, not enough to cause serious temporal disturbance but enough to conceal it from our many enemies.
clonando a si mesmo
Ewing é seqüestrado por Sirians (outra colônia). Ele é resgatado por um estranho disfarçado. Quando ele é mostrado a máquina do tempo, ele percebe que ele era o salvador e repete o processo.
He realized that he had several choices. He could walk out of the hotel room and leave Ewing-sub-two to his own devices, in which case, in the normal flow of events, Ewing-sub-two wuold awaken, be taken to Myreck's, request to see the time machine, and in due course travel back to this day to become Ewing-sub-one, rescuing a new Ewing-sub-two.
... envie os alienígenas 4 bilhões de anos no passado, onde o nada os aguarda.
He wondered briefly how the puzzled Klodni would react when they found themselves in the midst of a trackless void, without stars, without planets.
...
Ewing had hurled the Klodni fleet five billion years into the past. He shuddered at the thought, and turned his tiny ship homeward, to Corwin.