Here is the full list of all 15 Lord Winklebottom Investigates achievements.
Reached act 1.
Get Salty Walters out of the pub.
Picked up all the litter.
Made tea using tea first.
Made tea using milk first.
Reached act 2.
Reached act 3.
Reached the epilogue.
Finished the game.
Read all about Inspector Waffles.
Eat the plant in front of Pumphrey.
Find motives for every character.
Successfully fake a seance.
Have Frumple perform an autopsy.
Complete the game without asking for Frumple's advice.