A long time ago.

the sky was darkened by a massive alien object which sped over the eastern horizon. 'What do you think?' I asked. 'I've seen it before.' The first words he'd spoken since we'd left the Wild West of the past. 'I can't explain it, but I know that it's the same ship I saw on my first mission, the one that shot me down. They've been watching us all the time, and now they're going to do something.' 'Listen, we're going to get out of here,' I told him. 'We need to find another place to hide.' 'What are you talking about? We're not going anywhere!'

'I have a plan. I've been thinking about it, and I know a place where we can go.' 'Where?' 'It's a planet, close to a star. The sun is the only source of power and light. The place is huge, and I've only ever been there once, but it's the best I can come up with at the moment.' 'Where is it?' 'Not far from here. They call it Earth.' 'Earth? You've been there before?' 'Yes. A long time ago.