I noticed I wasn’t invited to sit this time. Lord Ashcombe loomed over me. “Explain yourself.”

I still didn’t really understand what I’d done wrong. “My lord?”

“What were you doing in the Berkshire House cellar?”

“We were… uh… looking for a rat.”

“A rat?”

The king laughed. “Oh, this I have to hear.”

I told them everything. About solving the puzzle with Walsingham this morning, then finding the second riddle in the Banqueting House. I explained how that had led us to Saint Paul’s, and how I’d been attacked. I gave Lord Ashcombe the assassin’s dagger, then showed them all the final letter, and what we thought it meant: that the king was to be poisoned at tomorrow night’s party with arsenic, which had already been mixed with the powdered sugar. Probably.

They all exchanged silent glances.

“Where is this sugar now?” Lord Ashcombe said.

“Tom has it, outside, my lord.”

“So what was the rat for?”

Before I could answer, the spymaster spoke, in his soft, quiet voice. “To test if the sugar is poisoned.”

He stood and went to the door. Opening it, he spoke to one of the waiting servants, who brought the sacks in from Tom. The spaniels sniffed around him.

“The dogs, sire,” Walsingham said.

Charles understood. If one of them licked poisoned sugar… He ordered the guards to usher the spaniels out. The servant placed the sacks on the table and, after a quiet word from Walsingham, left.

“You don’t expect me to eat it, I hope?” the king said.

“A rat is coming,” the spymaster said.

I decided to chance asking. “M—” I caught myself just before saying Master. “My lord?”

Walsingham raised an eyebrow.

“Did we do something wrong? I don’t understand why everyone is so cross.”

“I’m not cross,” he said.

Lord Ashcombe snorted.

“Tell me,” the spymaster said, “what you think happened.”

“Well… we stumbled—totally by accident,” I emphasized, “on that secret passage. I’m assuming there’s something in there we weren’t supposed to see. Or even know about. Behind the iron door with all the locks.”

The king drained his glass of wine. “I’m so glad you’re on my side,” he said wryly. “Go on, tell him.”

“The passage is an escape tunnel,” Lord Ashcombe said. “It exits into a grove in Saint James’s Park. It was built during the Civil Wars, in case the house ever came under siege. Several of the homes around here have them, including the palace. As for the vault…”

He looked to the king for approval. Charles finished the sentence himself. “It’s a secret treasury. There’s quite a bit of jewelry in there at the moment, some forty thousand pounds’ worth.”

I glanced over at the spymaster. He said nothing, and his expression remained as blank as ever. But I was sure he was thinking the same thing I was.

They have guards going in and out of the cellar all day long. The guards know. The servants almost certainly know, too. So how secret can this vault be?