cal 'mantle of the phoenix'
You are already protected by the Mantle of the Phoenix.


 l
A Dark Mausoleum 
 
[Exits: north down]
(Invis) (Ghostly) Wrapped in a dark cloak, a sword-bearing
woman waits in the shadows.


 com 'detect e' 
You close your eyes and hum for an instant.
Righteousness floods through you as your eyes attune to the
auras of wicked things.


 l
A Dark Mausoleum 
 
[Exits: north down]
(Invis) (Red Aura) (Ghostly) Wrapped in a dark cloak, a
sword-bearing woman waits in the shadows.


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As seen, mantle is not detecting evil.

I think this happens when: 
detect evil is active
mantle is called
detect evil falls before mantle

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