"If I do not return within ten minutes or so, something went wrong." Jon gives the others a nod, then walks to the entrance. Once there, he begins to shrink, transforming into a rat, which proceed to skitter into the crypt.
Spoiler
Show
wild shape for pest form, 10 minutes, costs 1 focus point

AC 16
Speed 10
Weakness 5 to physical damage
Low-light vision and imprecise scent 30 feet.
Acrobatics and Stealth modifiers of +10
Athletics modifier –4

Perception checks are secret, modifier is +6

Exploration activity is avoiding notice

Will go as far as possible in checking the area near the entrance, moving further in until time runs out, accessible space runs out, or he encounters opposition that can not be easily circumvented. Or finds a situation that requires immediate intervention or reporting.