Mary Roberts Rinehart 
When a Man Marries [PDF ebook] 

When a Man Marries is a classic screwball comedy – complete with a feisty female lead, mistaken identities, romance, witty repartee and a cast of befuddled high-society types. Jewelry thefts and mysterious happenings are part of the plot.
Kit Mc Nair just wants to help a friend distraught over the approaching second anniversary of his divorce. She encourages Jimmy Wilson to host a small dinner party at his fashionable New York home. As the group gathers, a frantic Jimmy informs them his wealthy Aunt Selina is coming for an unexpected visit. Aunt Selina disapproves strongly of divorce – and she holds Jimmy's purse strings. The rest of the group persuades the reluctant Kit to pose as Jimmy's wife, just for the duration of Aunt Selina's short stay.
Of course, a whole host of complications ensue. Jimmy's butler falls ill with what appears to be smallpox, and the rest of the frightened servants flee the house. Jimmy's REAL ex-wife, Bella, shows up unannounced, forcing Kit to hide her in the basement. Then the public-health authorities arrive to lock up the entire dinner party in quarantine.
Thus the stage is set for an outrageous, wild romp. Used to being fed and dressed by servants, the trapped guests muddle along as best they can. Aunt Selina unleashes her domestic tyranny on the household. Jimmy tries to give Bella the cold shoulder, but it soon becomes obvious he still adores her (all while he's supposed to be playing the part of Kit's devoted husband). And while pretending to be Jim's wife, Kit finds herself increasingly attracted to a handsome new acquaintance, Tom Harbison, an engineer with little use for the "non-producing parasites" of the upper crust.
There's also a romantic thread. It's rather funny, as each is baffled by the lies they began to tell at the beginning of the ill-fated dinner party. It's definitely a good lesson on what horrid complications can result from a "tiny bit of help to a friend, " otherwise known as a great lie.