A friend and I went on a garden tour, and I snapped photos of plants that neither my friend nor the garden owners could identify. All of the plants are in Zone 6 gardens in west-central Ohio. This one reminds me of a cross between lychnis and nicotiana. It's a little wild-looking, but it's blooming and seems happy in full sun. The flowers have no fragrance. The entire plant is about 18" tall.
SOLVED: Unknown plant on a garden tour
That's a close match. The differences are in the size of the flowers (this plant's flowers were rather small) and the color of the "bladder" (Silene alba has reddish striping while this one has no red at all). Perhaps those differences are due to sun exposure or geographical location. Thank you for zeroing in on this one.
Compared to the size of the hand in your photo, your plant has rather large flowers. Yes, striping on the "bladder" for many silenes is very dependent on sun exposure.