To learn secret Knowledge, you will need Soul Shard items. You can get them:

• For killing enemy warriors from foreign Kingdoms
• For destroying neutral troops that defend Towers of Fury
• For destroying troops led by jötunns during a Stronghold siege

The number of all the Soul Shards that you have is displayed in Resources section of the My Items tab.

The upgrade cost for secret Knowledge starts at the same level in all categories. After upgrading Knowledge in one category, the upgrade cost for the remaining categories increases to the next level.

After the first upgrade of secret Knowledge in one category (let's say you choose the Attack branch), the cost for secret Knowledge in the other categories (Defense and Fortresses) increases to the second level.

When you upgrade secret Knowledge in the next category, the upgrade cost for Knowledge in the remaining category increases. E.g. you learned Attack and decided to learn Knowledge from the Defense branch next. In this case, the upgrade cost for the Fortresses category increases to the third level.

If you started learning the first secret Knowledge in any category and thus the cost level of the remaining categories increased, and then canceled this process, the cost levels will return to their initial state. However, the Soul Shards you spent won't be returned.

For example, let's say you decide to learn the first Knowledge in the Attack category. At this point, all three categories are still at the first cost level. When you start learning, the cost of the secret Knowledge in the Defense and Fortresses categories will increase to the second level. If you change your mind and cancel the process, the cost level in the Defense and Fortresses categories will reset to the first level.

Think carefully about which category of secret Knowledge you should choose first — its upgrade cost will be substantially lower.

Please note: the higher the cost level, the more Influence and Hero's and Shaman's experience you will get for learning Knowledge.

To upgrade secret Knowledge, you need to hit its icon and choose how you want to perform the upgrade: instantly for Gold or over time in exchange for the Soul Shards.

Various boosts, VIP status, and other bonuses affect secret Knowledge in the same way as main Knowledge.

Remember, that you can upgrade only one Knowledge at a time, or two at a time with a special Prophet item.