The case opens at The National Gallery in central London and moves west and south from there. On foot the route takes in Piccadilly Circus, the approach to Buckingham Palace, and the stretch along to Westminster Abbey and Big Ben. It is a detective murder mystery walking tour through the part of London most people only cross at speed.

The pavements here are busy and the crossings are slow, so expect a London walk that stops and starts. Teams are up to four people sharing one phone; larger groups run as several teams and meet up afterwards, and playing alone is perfectly workable. No guide leads the way and no start time is fixed, so you can begin whenever the rest of your day allows. Crowds thin out on the side streets, which is where a good part of the route runs.

How to play

Four steps stand between booking and your first clue.

1. Book the City Game
2. Check the instructions email
3. Download the Loquiz app
4. Start playing whenever you like

The murder of Balthasar is the case you take on. Coded messages, photo tasks and statements from digital characters come in as you go, and few of the accounts agree with each other. Between Westminster Abbey and the streets running back towards Piccadilly Circus the suspect list gets shorter.

Set several teams going at once and it becomes a race, which is why it works as teambuilding as well as a day out. Stop for lunch, pick the trail back up, and close the case in London whenever you decide to.