Up in Mabel's Room is a 1944 American comedy film directed by Allan Dwan and starring Marjorie Reynolds, Dennis O'Keefe and Gail Patrick.

[2] Engineer Gary Ainsworth (Dennis O'Keefe) is about to celebrate one month of marriage to his wife Geraldine (Marjorie Reynolds), when his ex-girlfriend Mabel Essington (Gail Patrick) contacts him.

As he exits the taxi he leaves the gift behind, wishing to be rid of it, but Mabel delivers it to his apartment and threatens to show it to his wife if he doesn't reveal that they had a romance in Mexico City.

For a sum of money, Gary gets the waiter and manservant Boris (Mischa Auer) to sneak into Mabel's room and steal the slip back from her.

The slip falls out of the pocket while Gary is dancing with his wife, and he quickly stuffs it down a vase to avoid discovery.

The next day Gary is sitting alone and abandoned in the library when Martha comes in carrying her maid's sister's baby in her arms.

Martha tells Gary she has disposed of the slip by giving it to her maid Priscilla (Jane Lambert) as a wedding gift.

Gary and Boris make one last attempt to retrieve the slip by crashing the wedding, and they accidentally interrupt the ceremony.

[4] This meant the film – which was to star Ilona Massey and Louis Hayward and be made after Twin Beds[5] – took longer to make than anticipated.