Firstly, when the PCs discover the time machine and the principles of its operation, they might be tempted to make a short trip to the Cretaceous, to avoid potential problems with recharging the capacitor bank from the diesel generator. This is a goose chase of the wildest kind, since the virus and its associated antibodies can only be found in Jurassic dinosaurs. If the PCs are familiar with the fact that only Ornitholestes seem to be carriers of the virus, the GM should make a secret roll against Common Sense or Paleontology for any appropriate characters and drop heavy hints on a successful roll.
If the PCs are smart enough to make their initial trip to the Jurassic to capture Ornitholestes, events will conspire to force them to make another trip into the past when they return. These events will be explained in detail in a following section.
When the PCs make the trip to the Jurassic to capture an Ornitholestes, they will have about a day of capacitor recharging from the diesel generator before they can return to the present. Nothing untoward will happen to the generator or fuel supply, unless the PCs specifically do something dangerous in the vicinity.
The time of day upon arrival in the past is essentially random, but for this trip the PCs will arrive about mid-morning, allowing them to spend most of the day hunting. If the players are not thinking, they may assume they arrive during daylight by default, which will increase their surprise later.
The hunting expedition will be challenging, but not seriously dangerous unless characters act stupidly. Some encounters with large dinosaurs, particularly Stegosaurus, should be used for colour, but the PCs should be able to avoid any fighting until they find a group of Ornitholestes. When they do find some, it will be a family group of 12 adults, protecting several hatchlings. Any animal-loving characters should experience some reluctance about killing any of the group, but it may be necessary! In order to extract enough fresh antibodies, a live animal must be brought back from the past. Fortunately the time machine is equipped for capturing and caging animals.
Eventually, the animal will be captured, the capacitors recharged, and the characters can make the jump back to the present.
Whatever happens in the past, one very important event must be engineered by the GM for the sake of the next part of the adventure. The PCs must somehow lose a piece of modern day equipment, leaving it behind in the past when they return to the present. What this piece of equipment actually is is not important, so the GM is free to allow the flow of the game and whatever encounters occur dictate something suitable. If a character loses a limb or hand in a particularly violent dinosaur encounter, the lost body part can serve just as well, so long as it is not recovered. The important thing is that the lost item will become fossilised, so scraps of cloth are not enough. Bones or anything made of metal will do fine. If nothing else, the characters will probably lose some bullets.
Upon opening the doors of the time machine, the first thing they will notice is that they are no longer inside the hangar building. The second thing they notice is the ruined city sprawling all around them.
The PCs have returned to an alternate timeline, produced by their activities in the past. They are still in the same location in Montana, but in this present there is a heavily bombed city covering the area. This will require a fright check for all characters except the most stoic, as soon as they realise what they have done.
The most obvious solution to this problem is to go back in time again to somehow undo whatever they did that caused such a radical change in history. This raises three important questions: What exactly did they do to change history? How can they control their time jump precisely enough to appear at the right time to undo it? And how on earth are they going to recharge the time machine, with no mains power and not enough diesel fuel?
The first clue to this puzzle is that the ruins around them look like those of a human city. This means that history was not changed so drastically that humans never evolved. Following this line of thought, whatever the PCs did to change history didnít really affect anything until after the evolution of humans. The only way that something done more than 50 million years ago could affect human culture is if a relic of that past visit survived and was discovered.
At this point, the PCs should realise that the equipment they left in the past must have been discovered by people as fossilised relics, and this somehow affected humanity so much that the course of human history was altered. If the PCs don't realise this, they can discover the facts by exploring the ruined city around them (as they will have to do anyway, to get fuel) and stumbling across the remains of a library.
Next file: The Alternate Timeline.