Share the practical envelope of the surprise
Give the guest the approximate departure and return times, whether they need to dress for outdoors, what food is available, and how long they will sit, stand or walk. A two-hour seated show may be a delightful surprise for one person and impossible for another on that particular evening.
Keep the reveal separate from consent
A useful invitation sounds like “I planned something indoors on Thursday from six until about ten. There is a two-hour seated part. Would you like to come, and is there anything I should check first?” The guest can decline, request details or ask for a different time without having to guess what they are agreeing to.
Make a version that can change
For a surprise evening show, “indoors, seated for two hours, home around ten” preserves the reveal. If access, food, or personal comfort depends on knowing more, share more. A surprise is successful only if the guest can participate comfortably.
If the guest needs to know the venue to assess access or food, tell them. Preserve another part of the surprise, such as the seat choice or a shared meal afterward. When a fixed ticket cannot change, check the necessary constraints before buying it. A secret detail should never become the reason somebody cannot participate.