Inside Source

When Inside Source enters, create a 2/2 white and blue Detective creature token.
{3}, {T}: Target Detective you control gets +2/+0 and gains vigilance until end of turn. Activate only as a sorcery.

Petrify

Enchant artifact or creature
Enchanted permanent can't attack or block, and its activated abilities can't be activated.

Seasoned Consultant

Whenever you attack with three or more creatures, Seasoned Consultant gets +2/+0 until end of turn.

Case of the Pilfered Proof

Whenever a Detective you control enters or is turned face up, put a +1/+1 counter on it.
To solve — You control three or more Detectives. (If unsolved, solve at the beginning of your end step.)
Solved — If one or more tokens would be created under your control, those tokens plus a Clue token are created instead. (It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Auspicious Arrival

Target creature gets +2/+2 until end of turn. Investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")

Plains

Thinking Cap

Equipped creature gets +1/+2.
Equip Detective {1}
Equip {3} ({3}: Attach to target creature you control. Equip only as a sorcery.)

Marketwatch Phantom

Whenever another creature you control with power 2 or less enters, Marketwatch Phantom gains flying until end of turn.

Make Your Move

Destroy target artifact, enchantment, or creature with power 4 or greater.

Novice Inspector

When Novice Inspector enters, investigate. (Create a Clue token. It's an artifact with "{2}, Sacrifice this artifact: Draw a card.")