Here is the full list of all 15 If On A Winter's Night, Four Travelers achievements.
FInish Act IV.
Finish Act III.
Examine all the shelves in the library.
Check in on Mrs Williams on the Other Side.
Give Mr Williams his morphine.
Finish Act II.
Read all the books in the parlour.
Play the harp.
Finish Act I.
Call Patrick a cab.
Give Patrick back his watch.