In case you're wondering why I don't start these stories, I have enough stories that are barely updated! How about this: A mom's night out party runs into trouble: They could run afoul of a powerful woman at a bar or nightclub who thinks one of the group "stole" her man, or a naughty mind controller, a vengeful ex-husband or rival. It could be non-consentual, MC, bondage, MILF....
An alternate concept, but related, it doesn't run into "trouble" per-say, but they achieve exactly what they hoped, seducing a couple of guys for a wild night of anonymous sex! Could be 'Group Sex' or 'MILF', depending on if the moms are angling for an orgy or each having their own boy-toy for the night. For both of those, I assume the moms are all single parents. Could also be 'Swingers' if this is a kind of mutually understood "One night a month we take off our rings and go have an adventure, but you damned well better use protection!" thing with their husbands... EDIT: My reasons for not doing this one myself are the same as Wicker.