Cloak & Dagger

Cloak & Dagger is a companion perk in Fallout 4.

Obtaining
To gain the perk, the Sole Survivor must reach maximum affinity with Deacon.

Effects
The player character gains +20% sneak attack damage and the duration of effects of Stealth Boys are increased by +40%.

Bugs

 * The bonus to the actual sneak attack damage multiplier on silenced weapons provided by this perk is known to behave erratically when interacting with Ninja and Mister Sandman. There does seem to be a bug with the calculations with all three perks active, depending on the order in which they were granted, as follows:

Sandman 3, Cloak, Ninja 3 = 6.3x Sandman 3, Ninja 1, Cloak, Ninja 3 = 5.9x Sandman 3, Ninja 2, Cloak, Ninja 3 = 5.9x Sandman 3, Ninja 3, Cloak = 5.9x Ninja 3, Cloak, Sandman 3 = 6.3x Ninja 3, Sandman 3, Cloak = 6.3x Cloak, Sandman 3, Ninja 3 = 6.3x Cloak, Ninja 3, Sandman 3 = 5.4x (!)

Further testing needed, but right now the only solution appears to be selecting/receiving these perks in the "correct" order.