Fenchurch didn't have a plan at all. She had been convinced that John would be Arthur and that she wouldn't need any money to get a place to sleep, or to return to her temporary home. John decided that they should let her spend the night on the flat. Sherlock agreed because he was determined to find out more about this situation.
Sherlock had written on his website "When I've eliminated the impossible, whatever remains, no matter how mad it might seem, must be the truth." He was now facing a difficult situation. He had no reason not to believe in this woman's statements, but she was speaking nonsense. This entire thing about a ship and other planets and dimensions was driving mad a man who didn't even considered his own solar system to be relevant in his job. He would not sleep that night trying to find something that illuminated this awful mess. ¿And what about the picture? It was there, evidence, in front of his eyes. He would go to the lab at the hospital as soon as she left. He didn't dare to leave her with John. She seemed weird and insane, so he wouldn't risk something happening to John.
John was asleep, Fenchurch took the sofa, and Sherlock was in his room letting his mind go on overdrive in the middle of the night, when there is no one to disturb his reasoning paths. Suddenly, there were voices outside on Baker Street and then a single ring on the doorbell. It sounded like a client. He opened the door and he couldn't believe his eyes.
There was a funny man, with big blue eyes and messy hair similar to Sherlock's but in a lighter shade. He was wearing a very outdated suit, and he had a wide smile on his face. The other man was John. Well, he wasn't John, but he looked exactly like him. He was wearing pajamas and a robe. Sherlock's head stopped right there. He had never been so extremely confused in his entire life.
"Are you Sherlock Holmes" the first man asked.
"Yes. Who are you? Where do you come from? Come in please" Sherlock answered. He was absolutely not sure of what his next step should be, but the funny man and John's clone were very calmed and they went into the flat as if they were used to this situation, completely ignoring his puzzled look.
"My name is Ford Prefect and this is my friend, Arthur Dent. We expected to find a friend in here, or maybe, you will be able to find her for us. You have quite a reputation here in your earth. Don't worry; I don't think Vogons will destroy earth in every single dimension."
"Do you happen to have tea?" said Arthur.
"Who are you?" Now Sherlock was raising his voice. Other than that time during the case of the Hounds, he had never felt so lost and vacant.
In that moment two things happened. Fenchurch woke up, and she saw Ford and Arthur and she screamed and yelled and jumped and went to kiss Arthur. This kiss was well received, because he was the guy she had been looking for. John woke up because of the noise, and in that exact moment he saw Arthur and Fenchurch said "Oh God" and fainted.