Why not?

The next day, you find yourself re-reading the letter again. If it's a scam, it seems a lot of effort to go to, and you aren't sure exactly what they stand to gain. You try looking the Solicitor's firm up online, which is less than helpful. They don't have a website, and the only mention of them is a brief listing on some legal directory thing, which at least suggests they're legit.

You consider again that it might be some practical joke, perhaps one of your friends thought it'd be funny to make you waste your weekend on a wild goose chase. It would explain the lack of stamp and postmark on the envelope, and the hand-written missive within, but you don't know how they would have got headed paper from an actual legal firm.

A few days later, you are on the train to London, the letter in hand along with various forms of ID. There was no mention of it in the letter, but they must need you to prove you are who you say you are, surely? The address on the letter takes you to a small alleyway, round the corner from Temple tube station, and a dark wooden door next to a small brass plate which proclaims this the offices of Hohenheim and Flamel, LLP. There is a rope bell-pull just above the plate.