HL: A War Of The Worlds mod for Half-Life 2

Mankind was blissfully unaware of the alien race living far beneath the permafrost of Mars, unaware of the events that had transpired long before their primordial Australopithecine ancestors.
80 million years ago, when a Bussard Ramjet flew at relativistic speeds into the milky way. The deceleration engines lit up half the Solar System as it made its approach to Jupiter. Using the gas giant's enormous gravitational field to slow itself down further, it steered its great body towards the Earth.
Settling into a polar orbit of the planet, it studied the primitive creatures that dominated the surface. It soon deemed the to be unsuitable for colonisation at this point in time, taking samples for their database, leaving a probe on a small continent. Once again the engines sounded as it headed towards the planet that would someday be known as Mars.
It landed upon the planets uninhabited surface and unfurled its engines, burrowing into the ground, triggering the bio-mechanical Guardians. Ever faithful, it began building a small subterranean colony. Soon reanimated, its masters filled the colony and began work upon the planet. Their environment giving the planet a red glow.
Metals and water, among other resources, were mined to build and power a small fusion rocket. The probe that was initially sent to Earth showed the burgeoning of an intelligence, which grew and adapted rapidly. This needed to be stamped out if the masters were to successfully colonise the Earth.
The rocket was aimed at a dwarf planet, sacrificing it, in order to start a chain of reactions that would result in a colossal meteor striking Earth in about 15 million years. The debris from the planet would, as they calculated, pass close enough to cause a slingshot effect around various planets . In one instance the trailing rocks were caught in a planet's gravity, forming a ring.
The Bussard Ramjet thus had the rocket carry out its duties and begin the slow but inevitable series of gravitational perturbations. The masters, who grew impatient, ordered that they be sent to sleep and be resurrected once the dust had settled and the climate of the Earth re-stabilised after the impact. The Bussard Ramjet thus waited for a signal from the probe on the Earth that the impact had taken place.
For the Ramjet, the thousands of generations of the dinosaurs passed like mist in the early spring morning, and the time soon came when the impact took place. The probe sent its signal. The Ramjet felt a sense of triumph, but yet sorrow, for though it had achieved its primary objectives, and soon would pose little use to its Masters. Shortly the probe would send another signal asking that colonisation of the Earth to begin.
But a most unfortunate, unpredicted, event took place. The probe was exceptionally hardy, being even able to a survive meteor's impact, it was however immobile. Thus when the continent was suddenly torn open by a particularly powerful geological hot spot, smothering it by a kilometre of burning hot lava, it found that the signals it tried to send on every wavelength could not possibly reach the Ramjet.
The Ramjet was not provided with an intelligence varied enough to realise what had happened. So it lay dormant. Meanwhile on Earth, life was starting again. The creatures that had survived the impact, evolved at an alarming rate, growing in strength and intelligence with every passing century.
Earth soon had a fully formed intelligent race, capable of independent thought. No longer were they evolved by nature but by their own creations, rapidly advancing.
Mankind made great leaps in technology. Space exploration was inevitable. The Earth was drained of its recourses, forcing man to search for his new home among the stars. They looked to their neighbour, the mysterious red planet Mars. A colony was sent to investigate its atmosphere and environment.. Their conclusion; Mars was dead. Terraforming on a planetary scale was initiated, atmospheric processors were built and plants were introduced, giving Mars a new stable atmosphere. Mars could breathe once again, and with it, the awakening Martian race.

The invasion.

The Martian initial attack was swift and brutal. All contact with the colonists on mars was lost and they were presumed dead. The invasion took mankind by surprise and before any action could be taken most of their military strength had been destroyed. It was a precision attack and almost achieved complete annihilation. However man had grown used to hard times, used to fighting against extinction and impossible odds, through years of wars and destroying one another. Pockets of resistance stood their ground and fought, refusing to fade into the night.
Meanwhile, in underground labs and hollowed out mountains, the best minds were at work. Established long ago during mans darkest hour they have hid away, silently studying, building. Forgotten by the world, hidden from Martian eyes. These are the last strongholds of mankind, but the enemy is forever closing in, all labs are preparing for a breach……