I don’t remember when I started thinking of the calling card as a mechanism. It’s not something that existed during TWIDI’s early days, when access to the Market used to be straightforward (i.e you open the door attached to the basement door in Zeynel’s house, which is one of many hubs).

The card first appeared in the Bridge chaplette as something Alfred throws into the fire to summon a Ministry agent. We see it again used in the same way earlier in this Chapter. The mechanism shown here is an alternate one: you swipe it in between the gaps of a doorway like a credit card, which then summons a Ministry place. (There’s one more step required to make that summoning successful – a step that I will reveal in a future TWIDI chaplette)