Learn Turkish: Kutsal kitabı okuduktan sonra gizlice toplanmalıymışlar. - After reading the sacred book, they supposedly must gather secretly.

The verb toplanmak (to gather) takes the obligation suffix -malı (must / have to), followed by the hearsay suffix -mış (supposedly / I heard that). Together, they mean "supposedly they must gather." You use this combination when someone else tells you about a rule or requirement that you didn't experience directly.

Why use toplanmalıymışlar instead of toplamalıymışlar?

Toplamak means to collect or gather an object (like collecting apples or papers). Adding the -n suffix makes it toplanmak, which is reflexive and means to gather together as a group of people.

How is the word gizlice formed?

It comes from gizli, which means secret or hidden. Adding the suffix -ce turns it into an adverb, meaning secretly or in a secret manner.

Why is it okuduktan sonra instead of okumaktan sonra?

To say "after doing an action" in Turkish, you must use the verb root plus -dIktAn sonra. Even though sonra takes the ablative (-dan/-den) case, verbs specifically require this -dık structure first. So, "after reading" is always okuduktan sonra.

Why does kitap become kitabı here?

Kitabı (the book) is the specific object being read. Even though the action is inside the phrase okuduktan sonra (after reading), it still acts like a verb and forces its specific object into the accusative case. Also notice that the hard p softens to a b when the vowel -ı is added.