Making the Marauders

Remus Lupin has a secret. Few know, few would still care for him if his secret was revealed.
His three best friends soon get suspicious of what happens to Remus when he disappears every month. Eventually they piece together everything. Will they continue to run after danger and mysteries together with Remus, or will the trio be running after their former friend with pitchforks?

Entry for @eternal_potterhead 's One-Shot contest