It has a QR code which links directly to where you can buy tickets on Eventbrite where there is a reduced “Earlybird” price which runs until the end of the second week in April. The link to Eventbrite is also here:
https://www.eventbrite.co.uk/e/hound-of-the-baskervilles-sherlock-holmes-tickets-585798417837
Don’t worry if you prefer to speak to someone, the telephone booking office will be open from the 1st May.