他们共同策划写了一封信.用英语怎么说？

他们共同策划写了一封信.

Between them they concocted a letter.

between

prep. 在…之间，私下，暗中，在…中任择其一，来往于…之间；adv. 当中，中间；

例句
How big is the abyss between what you think you are and what you actually are?
你对自己的认识和真实的你之间差别到底有多大？

them

pron. 他们，她们，它们；

例句
I take care of them to the best of my abilities...
我尽我所能地照顾他们。

they

pron. 他/她/它们，人们，大家，政府，当局，她们；

例句
The storms had abated by the time they rounded Cape Horn.
他们绕过合恩角时，暴风雨已经减弱。

concocted

v. 将（尤指通常不相配合的）成分混合成某物( concoct的过去式和过去分词 )，调制，编造，捏造；

例句
Mr Ferguson said the prisoner concocted the story to get a lighter sentence.
弗格森先生说犯人捏造了这件事儿以求轻判。

letter

n. 信，证书，许可证，字母，文字，字面意义；vt. 用字母标明，写字母于，加标题；vi. 写印刷体字母；

例句
Naylor acknowledged, in a letter to the judge, that he was a drug addict...
内勒在给法官的信中承认自己吸毒。