Here is the full list of all 30 The Darkside Detective achievements. It takes around 6-8 hours to unlock all of the achievements on Windows.
Close case 7: Buy Hard
Fully explore the vents
Take a photo at the photobooth
Play games in arcade
Remember neglected responsibilities
Watch the credits to the end.
Close case 6: Don Of The Dead.
Examine 8 cars.
Use the kango hammer on everything in the sewers before advancing.
Search 10 bins.
Slack off the job and read a trashy mag in each case.
Close case 5: Loch Mess.
Enter the Cursed Lodge.
Take all of the Turner's calls in the Bloodwolf HQ.
Close case 4: Police Farce.
Listen to all of Dick Brickman's radio shows. Featuring Dick Brickman.
Give Laxatives to McKing.
Close case 3: Disorient Express.
Complete the virus minigame in three steps.
Listen to all of John's gags.
Spot the Darkside SkyBeast.
Close case 2: Tome Alone.
Read all the book titles in the library.
Close case 1: Malice In Wonderland.
Check Roy's Alibi