Sheer Folly

In March of 1926, Daisy Dalrymple Fletcher and her friend Lucy head off for several days at stately home reputed to have the best grotto in the country. Working on a book of architectural follies they plan to research and photograph it.
Leaving her husband and young twins behind, Daisy is expecting a productive weekend at Appsworth Hall, with the only potential difficulty being keeping Lucy from offending the current owner, a manufacturer of plumbing products. Alas, it's not to be quite so simple.
At the home, they find themselves faced with a curious assortment of people including the abominable, tactless Lord Rydal, who is rumored to be having an affair with one of the guests while at the same time in ardent and artless pursuit of the hand in marriage of another. When the grotto explodes with Lord Rydal in it, it's not a question of who would do it - as most who've met him would be sorely tempted - but who actually did do it.
Praise for the Daisy Dalrymple series:
'Cunning... appropriate historical detail and witty dialogue are the finishing touches on this engaging 1920s period piece.' Publishers Weekly
'As always, Dunn evokes the life and times of 1920s England while providing a plot that is a cut above the average British cosy. This will delight readers who love country-house mysteries.' Booklist
'For fans of Dorothy L. Sayers' novels' Library Journal