reason why you can play 'for free'

target of play 'for free'

Bajoran Resistance Cell
Seeds or plays on table. Once each turn, your Resistance personnel may report for free to your facility or ship or to any planet. Also, your Bajoran espionage cards may not be nullified. Once each turn, you may download a Bajoran espionage card to one to your missions (limit one per mission), then draw two cards if you have at least two Resistance personnel in play.

Furel, Gantt, Kira, Kira Founder, Kira Nerys, Lenaris Holem, Li Nalas, Lupaza, Orta, Razka Karn, Shakaar Edon, Surmak Ren, Tabor, Tahna Los

In For A Trim
Seeds or plays on table. Barber Pole and Mot’s Advice play for free. Once each turn, if you have Barber Pole in play, you may "take a little off the top": peek at the top X cards of opponent's draw deck, where X is the number of your non- Barbering personnel in play. You may discard any events, incidents, or interrupts (except and cards), then replace the rest in any order.

Barber Pole, Mot’s Advice

Plans of the Obsidian Order
Seeds or plays on table. Wherever you have an Obsidian Order personnel in play, your Cardassian espionage cards play at any time (for free) and may not be nullified. Also, once each turn, you may discard one of your Cardassian espionage cards from hand or table, then draw one card. At any time you may discard this objective from table to download one Cardassian espionage card.

Espionage: Cardassian on Bajoran, Espionage: Cardassian on Federation, Espionage: Cardassian on Klingon

Plans of the Tal Shiar
Seeds or plays on table. Wherever you have a Tal Shiar personnel in play, your Romulan espionage cards play at any time (for free) and may not be nullified. Also, once each turn, you may discard one of your Romulan espionage cards from hand or table, then draw one card. At any time you may discard this objective from table to download one Romulan espionage card.

Espionage: Romulan on Bajoran, Espionage: Romulan on Cardassian, Espionage: Romulan on Federation, Espionage: Romulan on Klingon

Revenge is a Dish Best Served Cold
Seeds on table during facility phase; you may download U.S.S. Reliant. Once each turn, your Khan (or any personnel with his name in lore) may report for free aboard U.S.S. Reliant; at end of every turn, you must discard all other personnel you have in play. At start of each of your turns, if your Khan and The Genesis Device are aboard U.S.S. Reliant, score 30 points (only 15 if opponent has any Kirk in play).

Joachim, Khan, Mas’ud, Sarod, Wajahut